RFR: 8253962: Add @ValueBased to unmodifable Collection implementation classes [v2]

[Roger Riggs]

> As per JEP 390, The implementations of ImmutableCollections are marked as being @ValueBased.

Roger Riggs has updated the pull request incrementally with three additional commits since the last revision:

 - remove blank line
 - Merge branch 'valuebased-collections-8253962' of https://github.com/RogerRiggs/valhalla into valuebased-collections-8253962
 - 8253962: Add @ValueBased to unmodifable Collection implementation classes

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Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/267/files
  - new: https://git.openjdk.java.net/valhalla/pull/267/files/d2891569..b6d88175

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=valhalla&pr=267&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=valhalla&pr=267&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/267.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/267/head:pull/267

PR: https://git.openjdk.java.net/valhalla/pull/267