RFR: 8315781: Reduce the max value of GCDrainStackTargetSize [v2]

[Albert Mingkun Yang]

> Simple adjustment to the max value of `GCDrainStackTargetSize`.
> 
> I picked 8K because the default queue capacity is ~16K and G1 use 2x of `GCDrainStackTargetSize` as some threshold.

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  Update src/hotspot/share/gc/shared/gc_globals.hpp
  
  Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15590/files
  - new: https://git.openjdk.org/jdk/pull/15590/files/6104cf26..ba16c5f4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15590&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15590&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15590.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15590/head:pull/15590

PR: https://git.openjdk.org/jdk/pull/15590