RFR: 8340818: Add a new jtreg test root to test the generated documentation [v7]

[Nizar Benalla]

> Please review this change that adds a new test root `docs` dedicated to testing the documentation, which has been a work in progress for a while. Tests for links, encoding, HTML, accessibility will be later added in following PRs. 
> 
> We also define a new make target `test-docs` meant for local use and depends on the docs.
> This also adds the necessary configurations needed at Oracle.
> 
> This patch includes a test `TestDocs` which serves to show developers how they are meant to resolve the docs to test them, I want to include it temporarily until better tests are added later.
> 
> TIA

Nizar Benalla 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 109 additional commits since the last revision:

 - Merge branch 'master' into 8340818-jtreg-test-root
 - 8341471: Reversed field layout caused by unstable sorting
   
   Reviewed-by: jwaters, jsjolen
 - 8341893: AArch64: Micro-optimize compressed ptr decoding
   
   Reviewed-by: aph, fyang
 - 8341708: Optimize safepoint poll encoding with smaller poll data offset
   
   Reviewed-by: kvn, qamai
 - 8336726: C2: assert(!do_asserts || projs->fallthrough_ioproj != nullptr) failed: must be found
   
   Reviewed-by: chagedorn, kvn, vlivanov
 - 8226938: [TEST_BUG]GTK L&F: There is no Details button in FileChooser Dialog
   
   Reviewed-by: honkar, prr
 - 8226933: [TEST_BUG]GTK L&F: There is no swatches or RGB tab in JColorChooser
   
   Reviewed-by: aivanov, psadhukhan, tr
 - 8341138: Rename jtreg property docker.support as container.support
   
   Reviewed-by: sgehwolf, mseledtsov
 - 8342003: ProblemList sun/security/tools/keytool/GenKeyPairSigner.java
   
   Reviewed-by: jpai
 - 8341797: Fix ExceptionOccurred in jdk.jdi
   
   Reviewed-by: amenkov, cjplummer
 - ... and 99 more: https://git.openjdk.org/jdk/compare/0e64a1e5...2c61ba76

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21272/files
  - new: https://git.openjdk.org/jdk/pull/21272/files/69ef43e4..2c61ba76

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21272&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21272&range=05-06

  Stats: 47666 lines in 758 files changed: 40684 ins; 3821 del; 3161 mod
  Patch: https://git.openjdk.org/jdk/pull/21272.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21272/head:pull/21272

PR: https://git.openjdk.org/jdk/pull/21272