RFR: 8339205: Optimize StackMapGenerator [v2]

[Shaojin Wen]

> Reduce code size by combining calls and defining local variables

Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 13 commits:

 - reduce codeSize
 - reduce codeSize
 - decStack & stackUnderflow
 - fix merge error
 - Merge branch 'master' into optim_stack_map_gen_202408
 - Merge remote-tracking branch 'upstream/master' into optim_stack_map_gen_202408
   
   # Conflicts:
   #	src/java.base/share/classes/jdk/internal/classfile/impl/StackMapGenerator.java
 - Merge remote-tracking branch 'upstream/master' into optim_stack_map_gen_202408
   
   # Conflicts:
   #	src/java.base/share/classes/jdk/internal/classfile/impl/StackMapGenerator.java
 - fix merge error
 - Merge remote-tracking branch 'origin/optim_stack_map_gen_202408' into optim_stack_map_gen_202408
 - optimize for codeSize
 - ... and 3 more: https://git.openjdk.org/jdk/compare/3f420fac...b647a4b5

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Changes: https://git.openjdk.org/jdk/pull/20756/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20756&range=01
  Stats: 363 lines in 2 files changed: 225 ins; 39 del; 99 mod
  Patch: https://git.openjdk.org/jdk/pull/20756.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20756/head:pull/20756

PR: https://git.openjdk.org/jdk/pull/20756