Overhaul DefaultInitExp

[dkorpel]

Big PR, will split off parts but first see how test suite reacts.

Probably fixes (edit: not yet) #18670 (needs tests), supersedes #14309

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[dkorpel]

/buildkite/builds/geod24-main-3/dlang/dmd/buildkite-ci-build/distribution/bin/../imports/std/process.d(798,41): Error: `@safe` function `test.executeCommand` cannot call `@system` function `std.stdio.makeGlobal!"core.stdc.stdio.stderr".makeGlobal`
                 File stderr = std.stdio.stderr,

Yep, that's a bug fix and a breaking change, will require either an edition guard or a deprecation.

[Herringway]

Glad to see this hole finally getting patched!

[thewilsonator]

Test suite looking good, ping me when this is good to go.

[dkorpel]

So I marked this PR as a refactor, switching from inlineCopy + resolveLoc to syntaxCopy + expressionSemantic. In more detail:

• Implement syntaxCopy for DefaultInitExp (the default syntaxCopy also copies the type which makes expressionSemantic quit early)
• Remove inlineCopy for default arguments, use syntaxCopy instead
• Remove subclasses / enum EXP members for each __FILE__ __LINE__ etc. token, and give DefaultInitExp a TOK to differentiate it instead
• Replace the resolveLoc() visitor with doing it directly in expressionSemantic
• Add call site location callLoc to the Scope struct, next to callsc, which expressionSemantic uses to resolve locations like resolveLoc did before.

This means less class boilerplate, not having a separate visit pass for resolveLoc anymore, and removing a weird dependency on inline.d. Since I wouldn't want to bury a bug fix in this big refactor, I disabled attribute checks for default arguments with:

    if (sc.inDefaultArg || sc.callLoc.isValid)
        return false;

In a follow up PR I plan to replace these with actual deprecation / edition logic to fix the bug, and add a test and changelog. If this all sounds good, it's ready to merge @thewilsonator

[thewilsonator]

I'll leave it to you to squash or rebase and merge as you see fit.