RFR: 8224922: Access JavaFileObject from Element(s) [v17]

[Joe Darcy]

> Initial review to get some comments on the shape of the API. Tests are needed of course, as well as some tuning of the spec to better describe differences in behavior when class files rather than source files are the backing file type.

Joe Darcy 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 42 additional commits since the last revision:

 - Merge branch 'master' into JDK-8224922
 - Merge pull request #7 from lahodaj/JDK-8224922-5
   
   Fixing a test on Windows.
 - Attempting to fix a Windows test.
 - Merge pull request #6 from lahodaj/JDK-8224922-4
   
   Adding forgotten file/fixing test.
 - Adding forgotten file/fixing test.
 - Reflow paragraphs.
 - Fix spec typo; update copyrights.
 - Merge branch 'JDK-8224922' of https://github.com/jddarcy/jdk into JDK-8224922
 - Merge pull request #5 from lahodaj/JDK-8224922-3
   
   Adding tests for unnamed module/package and automatic modules.
 - Using a specific class file as the source.
 - ... and 32 more: https://git.openjdk.java.net/jdk/compare/63d998ea...55759b2f

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5038/files
  - new: https://git.openjdk.java.net/jdk/pull/5038/files/cd9f6bc5..55759b2f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5038&range=16
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5038&range=15-16

  Stats: 6775 lines in 268 files changed: 5202 ins; 514 del; 1059 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5038.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5038/head:pull/5038

PR: https://git.openjdk.java.net/jdk/pull/5038