RFR: 8252546: Move ObservableValue's equality check and lazy evaluation descriptions to @implSpec [v2]

[Nir Lisker]

> Moving implementation details about lazy evaluation and equality checking to `@implSpec`.

Nir Lisker has updated the pull request incrementally with one additional commit since the last revision:

  Addressed review comments

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/292/files
  - new: https://git.openjdk.java.net/jfx/pull/292/files/808ba3ce..2a0b1f3b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=292&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=292&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/292.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/292/head:pull/292

PR: https://git.openjdk.java.net/jfx/pull/292