Indentation of asssignment comments between lhs and rhs

[davidBar-On]

Backport of suggested R2 changes for handling indentation of comments between assignment rhs and lhs, taken from different R2 PRs/commits. Not all changes were merged into R2, so this is why I didn't add "Backport" to the title.

Test cases are backport of PR #4734 test cases (which are enhancement of PR #4661 test cases).

The PR is based on:

• Backport of R2 PR #4661 (merged into R2).
• Backport of R2 PR #4734 (not merged into R2).
• Changes based of backport of R2 changes to Rewrite for ast::Local done by this commit.
• Implementation of the R1.x PR #5480 (was not merged yet) changes to light_rewrite_comment() which were backported from R2, as the test cases require these changes for proper formatting.