RFR: 5021949: JSplitPane setEnabled(false) shouldn't be partially functional [v6]

[Prasanta Sadhukhan]

> Issue is seen in that if we call setEnabled(false) over JSplitPane than it can't be dragged via its divider, But if SplitPane have one touch expandable true than user can click those buttons and change the divider position. 
> So, if splitpane is disabled, then both dragging in divider and one-touch-expandable click should be disabled.
> Fix is made to override setEnabled and disable one-touch-expandable buttons actions..

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  Fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/19695/files
  - new: https://git.openjdk.org/jdk/pull/19695/files/a728acf7..26895e7a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19695&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19695&range=04-05

  Stats: 40 lines in 3 files changed: 2 ins; 23 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/19695.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19695/head:pull/19695

PR: https://git.openjdk.org/jdk/pull/19695