checkpatch: improve email parsing

checkpatch doesn't report warnings for many common mistakes in emails.
Some of which are trailing commas and incorrect use of email comments.

At the same time several false positives are reported due to incorrect
handling of mail comments.  The most common of which is due to the
pattern:

<stable@vger.kernel.org> # X.X

Improve email parsing in checkpatch.

Some general email rules are defined:

- Multiple name comments should not be allowed.
- Comments inside address should not be allowed.
- In general comments should be enclosed within parentheses.
  Relaxation is given to comments beginning with #.
- Stable addresses should not begin with a name.
- Comments in stable addresses should begin only
  with a #.

Improvements to parsing:

- Detect and report unexpected content after email.
- Quoted names are excluded from comment parsing.
- Trailing dots, commas or quotes in email are removed during
  formatting. Correspondingly a BAD_SIGN_OFF warning
  is emitted.
- Improperly quoted email like '"name <address>"' are now
  warned about.

In addition, added fixes for all the possible rules.

Link: https://lore.kernel.org/linux-kernel-mentees/6c275d95c3033422addfc256a30e6ae3dd37941d.camel@perches.com/
Link: https://lore.kernel.org/linux-kernel-mentees/20201105200857.GC1333458@kroah.com/
Link: https://lkml.kernel.org/r/20201108100632.75340-1-dwaipayanray1@gmail.com


Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
Suggested-by: Joe Perches <joe@perches.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>