[CodeCompletion] Support completion for macro roles and the 'names:' argument label

[ahoppen]

This PR contains two preliminary commits:

• First we need to pass the ParserStatus from attribute parsing through to decl parsing, otherwise we’re don’t know the delayed decl state in which we’re completing (for @available parsing we got away without this by making the code completion token part of the declaration but that doesn’t work for the parser’s implementation of macro roles)
• Disallow declaration of codeItem macros. Previously, it was perfectly fine to declare codeItem macros, you just couldn’t use them.

And finally, we can hook things up to perform suggest macro roles and the names: label in macro attributes.

rdar://108163121

[ahoppen]

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[rintaro]

It might not really matter, but there is "feature" flag for each macro roles e.g. CodeItemMacros, FreestandingMacros. Do we want to use them here perhaps?

[ahoppen]

Oh, I am using it for codeItem but I should also use them for freestanding declaration (and all the others even if the feature flags are off), you are right.

[ahoppen]

OK, putting those behind a feature flag failed because then we can’t compile the stdlib anymore. I suspect that the issue is that the features are only enabled if we have swiftSwiftParser but we don’t have that yet while building the stdlib during bootstrapping. I just reverted it to always enable non-codeItem macros – freestanding declaration macros don’t have a feature flag (rdar://108637367).

[ahoppen]

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