Improves the grammar, functionality, and code quality of set declarations

[Altoids1]

Summary

Fixes #751 by doing a bunch of facelifting of how set statements are constructed.

In fixing this, I ended up shotgun-debugging a lot of things surrounding how set statements are constructed. This PR also include some additional documentation added to various things, as I looked at them or touched them during development of this.

Changelog

• Fixes set declarations not respecting commas, indented blocks, nor bracing.
• Blocks now very consistently evaluate their set statements first and foremost, before anything else, in a way that makes sense
• Use of the in keyword is now properly prohibited for all set use cases except 'src'
• set src now properly gives an unimplemented warning
• Slightly optimizes DMASTProcBlockInner by reducing empty array allocations.
• Removes DMASTProcStatementMultipleVarDeclarations, and replaces it with DMASTAggregate<>.
• Makes Consume array overload return the TokenType if found

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[Altoids1]

This PR now correctly mimics the cursed behaviour BYOND has when a set statement's right-hand side is non-constant. This feature must be manually enabled through a #pragma directive.

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[ike709]

Fails CI, in case you didn't see the last run finish.

[wixoaGit]

This appears to be on an older version of RobustToolbox.

[Altoids1]

This appears to be on an older version of RobustToolbox.

Github Desktop is a useful tool for resolving merge conflicts