Switch to System.Text.Json

[pbiggar]

Several functions in Dark used JSON.Net, which supported some of the esoteric features of OCaml's Yojson, such as generating and parsing tokens like NaN and Infinity.

However, .NET is moving to using System.Text.Json, an idiomatic, extremely performant Json parser/serializer, that also plays nicer with Blazor.

JSON.Net has some differences with Yojson, and also introduces some surface area of its own. That means that moving to STJ via JSON.Net will probably introduce more problems that just going straight to STJ (even if STJ doesn't support some non-JSON-complaint things we were parsing/generating before).

This PR splits the JSON functions into internal (DvalReprInternal) and external (DvalReprExternal) ones:

• external ones are moving straight to STJ, and we need to warn users about the very minor differences (these have been added to the changelog)
• internal ones can safely be moved later without notifying users, so there's no reason to change now (and likely things will break if we do)

The work was tracked in #3127

Major changes:

• Formatting:
  • now using STJ:
    • toPrettyMachineJson
    • toPrettyResponseJson
    • ofUnknownJsonV0
  • Still using Json.Net:
    • toInternalQueryableV1
    • ofInternalQueryableV1
    • toInternalRoundtrippableV0
    • ofInternalRoundtrippableV0
    • LibJwt
  • Using something else:
    • BackendOnlyStdLib.LibHttpClient0.PrettyRequestJson.toPrettyRequestJson (just printing strings)
    • LibExecutionStdLib.LibObject.PrettyResponseJsonV0.toPrettyResponseJsonV0

Modules:

• now moved to DvalReprExternal:
  • json stuff (all using STJ)
    • toPrettyMachineJsonStringV1
    • ofUnknownJsonV0
  • other serializations
    • toDeveloperRepr
    • toEnduserReadableTextV0
  • misc web stuff
    • typeToBCTypeName
    • typeToDeveloperReprV0
    • toFormEncoding
    • ofFormEncoding
    • toQuery
    • ofQueryString
    • queryToEncodedString
    • toStringPairs
• now moved to DvalReprInternal:
  • hash
  • toInternalRoundtrippableV0
  • ofInternalRoundtrippableV0
  • toInternalQueryableV1
  • ofInternalQueryableV1
  • currentHashVersion
• now moved to other modules
  • BackendOnlyStdLib.LibHttpClient0.PrettyRequestJson.toPrettyRequestJson

Refactoring:

• removed {of,to}_internal_queryable_v0, which wasn't used anywhere
• inlined a bunch of functions for clarity:
  • ofUnsafeDvalV0 into ofUnknownJsonV0

Json testing:

• use standard compliant json on all tests
• be more exact on a lot of tests, don't just parse both as json
• fix representation of floats, especially -0.0
• enable dvalRepr and fuzz tests for PrettyRequestJson and PrettyResponseJson (Add fuzzing for PrettyResponseJsonV0.unsafeDvalToJsonValue #3266)

Misc Testing:

• update list of naughty strings
• test using the list of naughty strings
• added interesting strings
• remove BOM naughty string
• generate junit file for backend
• add timeouts to httpclient-based tests
• fix tests involving side-effecting
• only remove the last comment on a line
• add tests for 64-bit ints and overflow (Test integer overflow behaviour and document/changelog it #3376)
• add tests for strings on bytes (Validate that toString of Bytes work the same in F# as in OCaml #3260)