RFR: 8338834: Remove unused import declarations in java.compiler [v2]

[Pavel Rappo]

> Please review this simple cleanup. I tested it first by usual means, and then additionally compared documentation before and after the change.
> 
> How did I end up with this cleanup? I finally got tired of an eyesore which greyed-out unused imports in my IDE are. So I removed them as per IDE suggestion and then had some fun chasing bugs. Who would've thought that removing imports can be so painful?
> 
> During my bug chase, I created the following issues, from which you could guess the kind of bugs I ran into:
> 
>   * https://youtrack.jetbrains.com/issue/IDEA-358082/Import-of-a-symbol-referred-to-by-snippet-target-is-considered-unused
>   * https://youtrack.jetbrains.com/issue/IDEA-358073/Support-changes-in-documentation-inheritance
>   * https://bugs.openjdk.org/browse/JDK-8338833
> 
> And a bonus one:
> 
>   * https://bugs.openjdk.org/browse/JDK-8338838

Pavel Rappo has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into 8338834
 - Initial commit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20679/files
  - new: https://git.openjdk.org/jdk/pull/20679/files/fb3397fe..05f3e0cf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20679&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20679&range=00-01

  Stats: 4348 lines in 110 files changed: 3005 ins; 651 del; 692 mod
  Patch: https://git.openjdk.org/jdk/pull/20679.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20679/head:pull/20679

PR: https://git.openjdk.org/jdk/pull/20679