Swift macro testing

[mayoff]

This pull request converts all macro expansion tests to use the MacroTesting library from the swift-macro-testing package.

I want to do some cleanup and enhancement of SwiftGodot's macros. In particular I want to make @Export automatically infer hints for subclasses of Node and Resource (both built-in and user-defined) and provide better, type-safe syntax for other hints (like @Export(.range(0 ... 10, step: 2, .orGreater)) instead of @Export(.range, "0,10,2,or_greater")).

To facilitate that work, I propose this patch to migrate the macro tests to a much friendlier testing library. The swift-macro-testing library has several advantages over SwiftSyntaxMacrosTestSupport:

• It is much easier to create new test cases. The library can update the test case with in the actual macro output the first time a test is run.

• It is much easier to update test cases when we intentionally change the code generated by a macro. The library can update the test case by replacing the old macro output with the new macro output if you set record: failed in the assertMacro invocation.

• It is much easier to verify that diagnostics and fix-its emitted by a macro are attached to the correct part of the input. Check out testMacroNotOptionalDiagnostic in SceneTreeMacroTests.swift for a great example!

For a full explanation of the design of swift-macro-testing, check out these videos:

https://www.pointfree.co/collections/macros/testing-and-debugging-macros

The video pages include full hand-written transcripts in case you'd rather read than watch.

[mayoff]

To be clear, this patch does not add or remove any test cases, or change the inputs or outputs of any test cases other than fixing indentation.

[migueldeicaza]

Thanks for this patch, this one will take me more time to review, but I am also a little hesitant on bringing another external dependency.

[mayoff]

Perhaps it would be better to ignore this PR until I have some other improvements to offer that build on this change.