RFR: 8321124: java/util/stream/GatherersTest.java times out [v2]

[Viktor Klang]

> Renames GatherersTest to BuiltInGatherersTest for easier deduplication of GathererTest.
> 
> Fixes a test ordering issue in testMapConcurrentAPIandContract().
> 
> Adding increased maxOutputSize for Gatherer-related tests to improve debuggability.
> 
> Lowering the composition threshold of GathererTest.testMassivelyComposedGatherers to 256 to avoid SOE on low-specc:ed machines.

Viktor Klang has updated the pull request incrementally with one additional commit since the last revision:

  Only run the cancellation tests for mapConcurrent for the shorter streams to conserve resources

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16928/files
  - new: https://git.openjdk.org/jdk/pull/16928/files/3605f959..a4ab3469

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16928&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16928&range=00-01

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16928.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16928/head:pull/16928

PR: https://git.openjdk.org/jdk/pull/16928