RFR: 8369039: JDK-8348611 caused regression in Javac-Hot-Generate

[Archie Cobbs]

The refactoring in [JDK-8348611](https://bugs.openjdk.org/browse/JDK-8348611) caused a regression in compiler performance. In the the refactoring there were a couple of simple optimizations that were missed. When put in place, these seem to (mostly) address the performance issue.

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

Commit messages:
 - Remove drive-by tweaks that aren\t the real issue.
 - Avoid using LintMapper when knowing rootLint suffices.
 - Avoid unnecessary recursion in LintMapper.

Changes: https://git.openjdk.org/jdk/pull/27651/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27651&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369039
  Stats: 11 lines in 2 files changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27651.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27651/head:pull/27651

PR: https://git.openjdk.org/jdk/pull/27651