RFR: 8304146: Refactor VisibleMemberTable (LocalMemberTable) [v2]

[Pavel Rappo]

> Please review a change to clean up and simplify LocalMemberTable; a container to cache, classify, and provide efficient lookup for the return value of `TypeElement.getEnclosedElements()`.
> 
> While the change primarily targets internals of LocalMemberTable, it also affects its clients: in particular, code that handles JavaFX documentation. That code does not seem to be tested well (I filed a bug for that: JDK-8304170). To make sure I haven't broken anything, aside from usual testing, I also cloned [OpenJFX](https://github.com/openjdk/jfx) and built its documentation with javadoc before and after the change. Documentation bundles were identical.

Pavel Rappo has updated the pull request incrementally with two additional commits since the last revision:

 - Trivially rephrase TODO
 - Address feedback
   
    - renames simplename to simpleName
    - links to the relevant JBS issue from TODOs

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13044/files
  - new: https://git.openjdk.org/jdk/pull/13044/files/45001afd..6013787a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13044&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13044&range=00-01

  Stats: 8 lines in 1 file changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/13044.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13044/head:pull/13044

PR: https://git.openjdk.org/jdk/pull/13044