Summary:
This revision imports PG15 upstream commits for security fix CVE-2025-1094
 1. 703b3fd5de5d7bfe9cb3948601bc165da024256d
```
Add pg_encoding_set_invalid()

There are cases where we cannot / do not want to error out for invalidly
encoded input. In such cases it can be useful to replace e.g. an incomplete
multi-byte characters with bytes that will trigger an error when getting
validated as part of a larger string.

Unfortunately, until now, for some encoding no such sequence existed. For
those encodings this commit removes one previously accepted input combination
- we consider that to be ok, as the chosen bytes are outside of the valid
ranges for the encodings, we just previously failed to detect that.

As we cannot add a new field to pg_wchar_table without breaking ABI, this is
implemented "in-line" in the newly added function.

Author: Noah Misch <noah@leadboat.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Backpatch-through: 13
Security: CVE-2025-1094
```
 2. b1756da7541323eae07fe23eaad17ce12f20a56b
```
Specify the encoding of input to fmtId()
This commit adds fmtIdEnc() and fmtQualifiedIdEnc(), which allow to specify
the encoding as an explicit argument.  Additionally setFmtEncoding() is
provided, which defines the encoding when no explicit encoding is provided, to
avoid breaking all code using fmtId().

All users of fmtId()/fmtQualifiedId() are either converted to the explicit
version or a call to setFmtEncoding() has been added.

This commit does not yet utilize the now well-defined encoding, that will
happen in a subsequent commit.

Reviewed-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Backpatch-through: 13
Security: CVE-2025-1094
```

 3. 370c94d4cce179736f9a255779eb8e653e1edfb2
```
Fix handling of invalidly encoded data in escaping functions
Previously invalidly encoded input to various escaping functions could lead to
the escaped string getting incorrectly parsed by psql.  To be safe, escaping
functions need to ensure that neither invalid nor incomplete multi-byte
characters can be used to "escape" from being quoted.

Functions which can report errors now return an error in more cases than
before. Functions that cannot report errors now replace invalid input bytes
with a byte sequence that cannot be used to escape the quotes and that is
guaranteed to error out when a query is sent to the server.

The following functions are fixed by this commit:
- PQescapeLiteral()
- PQescapeIdentifier()
- PQescapeString()
- PQescapeStringConn()
- fmtId()
- appendStringLiteral()

Reported-by: Stephen Fewer <stephen_fewer@rapid7.com>
Reviewed-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Backpatch-through: 13
Security: CVE-2025-1094
```

 4. de4b92f3332b7ea3373ae7bad0d790473b3665e6
```
Add test of various escape functions
As highlighted by the prior commit, writing correct escape functions is less
trivial than one might hope.

This test module tries to verify that different escaping functions behave
reasonably. It e.g. tests:

- Invalidly encoded input to an escape function leads to invalidly encoded
  output

- Trailing incomplete multi-byte characters are handled sensibly

- Escaped strings are parsed as single statement by psql's parser (which
  derives from the backend parser)

There are further tests that would be good to add. But even in the current
state it was rather useful for writing the fix in the prior commit.

Reviewed-by: Noah Misch <noah@leadboat.com>
Backpatch-through: 13
Security: CVE-2025-1094
```

 5. 57bda2508f1c666fd18f2b233823b7c98308226b
```
docs: EUC_TW can be up to four bytes wide, not three
Backpatch-through: 13
Security: CVE-2025-1094
```

 6. a085fa73169d6c0df079cfa4ddfeade812368a64
```
Fix type in test_escape test
On machines where char is unsigned this could lead to option parsing looping
endlessly. It's also too narrow a type on other hardware.

Found via Tom Lane's monitoring of the buildfarm.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Security: CVE-2025-1094
Backpatch-through: 13
```

 7. 9862de9176ef161e20a40f327afe18c6a11ecdcc
```
Adapt appendPsqlMetaConnect() to the new fmtId() encoding expectations.
We need to tell fmtId() what encoding to assume, but this function
doesn't know that.  Fortunately we can fix that without changing the
function's API, because we can just use SQL_ASCII.  That's because
database names in connection requests are effectively binary not text:
no encoding-aware processing will happen on them.

This fixes XversionUpgrade failures seen in the buildfarm.  The
alternative of having pg_upgrade use setFmtEncoding() is unappetizing,
given that it's connecting to multiple databases that may have
different encodings.

Andres Freund, Noah Misch, Tom Lane

Security: CVE-2025-1094
```

 8. e782a63ccb76a8db476abb8f5d96397806e3e51b
```
Make escaping functions retain trailing bytes of an invalid character.
Instead of dropping the trailing byte(s) of an invalid or incomplete
multibyte character, replace only the first byte with a known-invalid
sequence, and process the rest normally.  This seems less likely to
confuse incautious callers than the behavior adopted in 5dc1e42.

While we're at it, adjust PQescapeStringInternal to produce at most
one bleat about invalid multibyte characters per string.  This
matches the behavior of PQescapeInternal, and avoids the risk of
producing tons of repetitive junk if a long string is simply given
in the wrong encoding.

This is a followup to the fixes for CVE-2025-1094, and should be
included if cherry-picking those fixes.

Author: Andres Freund <andres@anarazel.de>
Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us>
Reported-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://postgr.es/m/20250215012712.45@rfd.leadboat.com
Backpatch-through: 13
```

 9. 2226a2e266dbabc5597fff5f624b3fcd71ce5fa8
```
In fmtIdEnc(), handle failure of enlargePQExpBuffer().
Coverity complained that we weren't doing that, and it's right.

This fix just makes fmtIdEnc() honor the general convention that OOM
causes a PQExpBuffer to become marked "broken", without any immediate
error.  In the pretty-unlikely case that we actually did hit OOM here,
the end result would be to return an empty string to the caller,
probably resulting in invalid SQL syntax in an issued command (if
nothing else went wrong, which is even more unlikely).  It's tempting
to throw an "out of memory" error if the buffer becomes broken, but
there's not a lot of point in doing that only here and not in hundreds
of other PQExpBuffer-using places in pg_dump and similar callers.
The whole issue could do with some non-time-crunched redesign, perhaps.

This is a followup to the fixes for CVE-2025-1094, and should be
included if cherry-picking those fixes.
```

This revision also ports changes made to `conversion.sql` regress test to yb equivalent test `yb.port.conversion.sql`.

Jira: DB-15558

Test Plan: ./yb_build.sh --java-test 'org.yb.pgsql.TestPgRegressPgMiscIndependent#testPgRegressPgMiscIndependent2'

Reviewers: vkushwaha, jason, skumar, devansh.saxena, stiwary

Reviewed By: jason

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D42247