Add booleans about checked properties to compound statements

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#420

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This adds two Booleans about checked properties to compound statements:

• IsCheckedScope: is this semantically a checked scope?
• IsCheckedPropertyDeclared: was this information explicitly declared for the block (using _Checked { ... } or _Unchecked { ... }.

I extended AST dumps to include this information for compound statements. I specifically omit dumping information for the existing behavior (where there is no declared property and the scope is unchecked). I do this to avoid breaking any existing tests that depend upon ASTs not having this information. I think there's only one test that breaks, but there could be more.

I didn't update AST reading/writing to record this information. I opened issue #419 to track this remaining work.

This does reduce the number of statements allowed in a compound statement from 2^24 to 2^22. I think we can live with that for now.

Testing:

• Add new test that checks that AST dumps include this information.
• Passed automated testing.