RFR: 8341512: Optimize StackMapGenerator::processInvokeInstructions

[Shaojin Wen]

A small optimization for StackMapGenerator::processInvokeInstructions.

1. Use local currentFrame to avoid multiple getfields
2. remove Util.methodTypeSymbol(NameAndTypeEntry)
3. Use decStack instead of popStack to reduce array access in popStack
4. codeSize reduced from 277 to 262

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Commit messages:
 - use decStack instead of popStack
 - remove Util.methodTypeSymbol(NameAndTypeEntry)
 - optimize processInvokeInstructions

Changes: https://git.openjdk.org/jdk/pull/21344/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21344&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341512
  Stats: 20 lines in 10 files changed: 1 ins; 7 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/21344.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21344/head:pull/21344

PR: https://git.openjdk.org/jdk/pull/21344