feat: replace pg_catalog tables with common table expressions

[olavloite]

Replaces pg_catalog table references with common table expressions:

1. pg_namespace is added with two fixed entries.
2. pg_type is added with 14 fixed entries.

This setup can be used to add more pg_catalog tables that are needed by drivers / frameworks.

[codecov]

Codecov Report

Merging #331 (d21aa2b) into postgresql-dialect (8a587af) will increase coverage by 0.12%.
The diff coverage is 87.21%.

@@                   Coverage Diff                    @@
##             postgresql-dialect     #331      +/-   ##
========================================================
+ Coverage                 83.83%   83.95%   +0.12%     
- Complexity                 1531     1593      +62     
========================================================
  Files                       112      114       +2     
  Lines                      5232     5417     +185     
  Branches                    683      727      +44     
========================================================
+ Hits                       4386     4548     +162     
- Misses                      633      643      +10     
- Partials                    213      226      +13     

Flag	Coverage Δ
all_tests	83.95% <87.21%> (+0.12%)	⬆️

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Impacted Files	Coverage Δ
.../cloud/spanner/pgadapter/session/SessionState.java	99.03% <ø> (+1.36%)	⬆️
...dapter/statements/JdbcMetadataStatementHelper.java	79.89% <ø> (-0.11%)	⬇️
...oud/spanner/pgadapter/statements/SimpleParser.java	90.51% <72.30%> (-3.87%)	⬇️
.../cloud/spanner/pgadapter/statements/PgCatalog.java	92.59% <92.59%> (ø)
...loud/spanner/pgadapter/statements/TableParser.java	93.33% <93.33%> (ø)
...ud/spanner/pgadapter/metadata/OptionsMetadata.java	77.55% <100.00%> (+0.45%)	⬆️
...panner/pgadapter/statements/BackendConnection.java	90.67% <100.00%> (+0.04%)	⬆️
...spanner/pgadapter/commands/InvalidMetaCommand.java	100.00% <0.00%> (+20.00%)	⬆️

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