RFR: 8197991: Selecting many items in a TableView is very slow [v6]

[Abhinay Agarwal]

> This work improves the performance of `MultipleSelectionModel`  over large data sets by caching some values and avoiding unnecessary calls to `SelectedIndicesList#size`. It further improves the performance by reducing the number of iterations required to find the index of an element in the BitSet.
> 
> The work is based on [an abandoned patch](https://github.com/openjdk/jfx/pull/127) submitted by @yososs
> 
> There are currently 2 manual tests for this fix.

Abhinay Agarwal has updated the pull request incrementally with two additional commits since the last revision:

 - Format code and reduce test size
 - Add size assertion to test

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/673/files
  - new: https://git.openjdk.java.net/jfx/pull/673/files/741aa92f..30fb31c4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=673&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=673&range=04-05

  Stats: 16 lines in 3 files changed: 0 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/jfx/pull/673.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/673/head:pull/673

PR: https://git.openjdk.java.net/jfx/pull/673