RFR: 8306560: Add TOOLING.jsh load file

[Christian Stein]

This PR adds the `TOOLING.jsh` load file for being used in `jshell TOOLING` commands.

_Man page update is pending..._

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Commit messages:
 - Add `TOOLING` load file name into help messages
 - Add dedicated `TOOLING` test class
 - Include `TOOLING` in compound start test
 - 8306560: Add TOOLING.jsh load file

Changes: https://git.openjdk.org/jdk/pull/13609/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13609&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306560
  Stats: 165 lines in 6 files changed: 153 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/13609.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13609/head:pull/13609

PR: https://git.openjdk.org/jdk/pull/13609