End-of-line comments [tracking issue]

This is a high-level tracking issue for end-of-line comments and having them attach to the back of the previous token instead of being attached the front of the next token.

To be considered:
- if/else branch bodies
- case branch bodies
- (maybe?) tag arguments in types (`Tag --z\n a --x\n b --y\n`)
- (maybe?) let definition bodies
- (maybe?) top-level definition bodies

Already implemented:
- https://github.com/avh4/elm-format/issues/162
- [x] after record fields in types
- [x] after record fields in expressions
- [x] after values in list expressions
- [x] after values in tuple expressions
- [x] after entries in tuple types
- [x] union type definitions
- [x] after record fields in record updates
- [x] after record fields in record extension types
- [x] in function types
- [x] in binary operator expressions
- [x] in cons patterns

No files, tests, or entry points are named. Read the tracking issue and linked issue 162, then investigate the formatter's existing end-of-line comment handling for the listed if/else, case, tag-argument, let-definition, and top-level-definition cases; done means the relevant comments attach to the preceding token without regressing the already implemented cases.

Written by the indexing model from the issue text.