Add regex to dedent else and friends

[kimadeline]

For #6333

• Dedent else (and elif while we're at it)
• Remove unnecessary rule now that we introduced the indentationRules key

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• [n/a] Appropriate comments and documentation strings in the code
• [n/a] Has sufficient logging.
• [n/a] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [n/a] Test plan is updated as appropriate
• [n/a] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• [n/a] The wiki is updated with any design decisions/details.

[brettcannon]

Going through Python's grammar, here is the thinking:

Dedent the following line after the statement

• break
• continue
• pass
• raise
• return (although check if it still indents if an dangling/open [, e.g.

return [  # Does the following line still get indented (which is what we want)?

Indent the the following line after the statement

• \
• if
• while
• for
• try
• with
• def
• class
• async def
• async for
• async with

Dedent the statement line itself while still indenting the following line

• elif
• else
• except
• finally

[kimadeline]

Make sure #4241 and #3284 are not impacted

[ericsnowcurrently]

Mostly LGTM. Everything looks correct. I just have a few comments relative to helping out readers.

Grammar reviewed

[ericsnowcurrently]

Thanks!