System.Text.Json fixes

[andrewheumann]

BACKGROUND:

• There were some issues using the STJ version of Elements for client-side geometry generation
• There were also some issues building / code-generating hypar functions that worked correctly with STJ.

DESCRIPTION:

• Fixes enum code generation — STJ's JsonStringEnumConverter ignores [EnumMember] attributes, which means JSON from hypar containing enums was frequently failing to deserialize and not serializing with the correct member names. the JsonStringEnumConverter is replaced with Macross.Json.Extensions's JsonStringEnumMemberConverter.
• deserializing ProxyElements of types that were not loaded was throwing an exception.
• Adds a generic test that reads some example models (which were previously failing). Over time we can add more real models here to test.

TESTING:

• I tested by using this branch in tandem with elements/wasm-explore-fixes and explore/wasm-playground and testing client-side geometry generation on explore
• I also tested this branch in tandem with hypar/stj. Functions aren't working all the way yet, since we're basically forced to upgrade to .net 6.0 — but most codegen and local building/running is working.

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This change is 

[ikeough]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @andrewheumann)

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Elements/src/Serialization/JSON/ElementConverter.cs line 115 at r1 (raw file):

                            {
                                // This may occur if the object is a proxy of a type we don't have the class for. Fallback to `Element`.
                                genericType = typeof(Element);

Very nice.

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Elements.CodeGeneration/src/HyparFilters.cs line 56 at r1 (raw file):

        /// Strip the nullable annotation (?) from a type.
        /// </summary>
        public static string Removenull(string input)

Do we use this in this PR?

[andrewheumann]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @ikeough)

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Elements/src/Serialization/JSON/ElementConverter.cs line 115 at r1 (raw file):

Previously, ikeough (Ian Keough) wrote…

Very nice.

Done.

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Elements.CodeGeneration/src/HyparFilters.cs line 56 at r1 (raw file):

Previously, ikeough (Ian Keough) wrote…

Do we use this in this PR?

Ah, good catch — I was using it, but now it's no longer needed with the third-party Enum converter.

[ikeough]

Reviewable status: complete! 1 of 1 approvals obtained