RFR: Improving pattern handling for non-null types

[Jan Lahoda]

Fixes dominance for binding/any patterns whose types have a bang, attempting to improve parsing of patterns with emoticon, ensuring correct desugaring of patterns with emoticon, adding tests.

Include code done by @vicente-romero-oracle (https://github.com/openjdk/valhalla/pull/1884)

-------------

Commit messages:
 - Cleanup.
 - Improving pattern handling for non-null types; includes code by Vicente.

Changes: https://git.openjdk.org/valhalla/pull/1902/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1902&range=00
  Stats: 205 lines in 5 files changed: 182 ins; 17 del; 6 mod
  Patch: https://git.openjdk.org/valhalla/pull/1902.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1902/head:pull/1902

PR: https://git.openjdk.org/valhalla/pull/1902