[AST] don't break a doc comment with a regular comment

[QuietMisdreavus]

Resolves rdar://95307936

When a declaration has a regular comment between its doc comment and the declaration itself, that doc comment is lost:

/// This is documentation
// This is a comment
public func myFunc() {}

This PR changes the comment attachment rules to skip over ordinary comments instead of using them to break them apart like a blank line would.

Notably, this change surfaced a bug in the standard library documentation: The default implementation of the != operator in Equatable had a regular comment between the doc comment and the declaration, causing that documentation to be lost. (This is why i had to update the tests in test/SourceKit/DocSupport, because the documentation for != started showing up!)

[QuietMisdreavus]

@swift-ci Please test

[bnbarham]

Seems reasonable to me, thanks @QuietMisdreavus! I don't think I had any good reason for not doing this in 22f5983, probably just went with keeping the current behavior assuming there was a good reason for it.

[ahoppen]

Thank you. Makes sense to me

[QuietMisdreavus]

@swift-ci Please test