Expression tests and related issues

[wti]

As promised in #299, I filled in some of the expression tests, raising three kinds of issues:

Test helper

• The top-level method actExp(..) is to replace XCTest assertion directly.
  It identifies the first text delta and prints expected and actual cleanly for copy/paste. But it is relatively ungainly and not isolated, and there are likely diffing libraries that would do a better job. It can merge and work as-is, but I can clean it up per your preferences. I used it only in the new tests.

Three kinds of test issues

1. 3 tests fail due to JSON encoding differences, presumed due to locale differences

• I flagged these as expected fails. In the expected locale, these should be reported as unexpected pass.
• I can investigate whether JSONEncoder configuration will avoid locale-dependent behavior.

2. testAsyncExpression3(): fails when there is no network

• It's unclear if we should check and skip, or use a different async call that does not require a network.

3. The test testIdentifierExprSyntax() now refers to a quoted keyword (`class`). Let me know if something else was intended.

• The variable `class` is rendered as [-n-]{+cl+}a[-me-]{+ss+}. Is that correct?

Two implementation issues

1. optional string has quotes around the entire optional: "Optional(\"0\")"
2. inout variables are rendered constant (unusable) by macro expansion, resulting in compile errors.

Merging
Commits with aspects to investigate are marked DRAFT. Commits are designed to merge even if the issues above require changes (e.g., tests should continue to pass; the current behavior is accepted for now). Commits are also separated to isolate the issues above, to allow skipping a particular issue/commit. The goal was to enable the changes to be merged, with follow-on work scheduled in later tasks.

[wti]

Sorry, I can't see the logs for the failing Bitrise or Test checks. I tested on macOS 14 with 5.9. (It fails as expected on Linux due to missing Foundation API's and objc support.)

[kishikawakatsumi]

Thank you for the PR! I'll check back later.

[wti]

Sorry, please ignore the first commit to add .project to the .gitignore (cb6d4e...). (I've added that to my global configuration.)

[wti]

Please let me know if you'd like me to rebase or merge the branch.

[kishikawakatsumi]

No worries. I just can't take my time.

[kishikawakatsumi]

Thank you very much. It looks good to me. All tests are passing in my local environment, so if there is a problem when I run it on CI, I will fix it on my end.

[wti]

Thank you for your patience.

I rebased off main, removed the unnecessary commit, and removed the expected failures per request.

fyi, four tests in AssertTests are failing for me:

• testMagicLiteralExpression2
• testInitializerExpression
• testSelectorExpression1
• testSelectorExpression2

(XCode 15.0, swift 5.9.0, M1 Studio)

If I discover a solution for inconsistent tests, I'll make a separate PR.

Thanks!