RFR: JDK-8305885: Use ReadOnly*PropertyBase class where possible [v4]

[John Hendrikx]

> These changes use base classes for custom properties where possible for the `ExpressionHelper` logic instead of duplicating these each time.

John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:

  Fix review comment

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1092/files
  - new: https://git.openjdk.org/jfx/pull/1092/files/c95635be..b2d1434a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1092&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1092&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1092.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1092/head:pull/1092

PR: https://git.openjdk.org/jfx/pull/1092