RFR: 8330179: Clean up non-standard use of /** comments in `jdk.compiler`

[Jonathan Gibbons]

Please review a fix to preempt warnings that would otherwise be introduced by [JDK-8303689](https://bugs.openjdk.org/browse/JDK-8303689), which introduces a new `javac` lint warning to detect documentation comments in unusual places.

The majority of the warnings are caused by "box comments" beginning with `/*****`. To minimize change and to address these, the second `*` is replaced by a space. An alternative solution might be to change the overall style of the box comment to use something like `/*---------`

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

Commit messages:
 - JDK-8330179: Clean up non-standard use of /** comments in `jdk.compiler`

Changes: https://git.openjdk.org/jdk/pull/18767/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18767&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330179
  Stats: 51 lines in 15 files changed: 0 ins; 0 del; 51 mod
  Patch: https://git.openjdk.org/jdk/pull/18767.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18767/head:pull/18767

PR: https://git.openjdk.org/jdk/pull/18767