RFR: 8341141: Optimize DirectCodeBuilder

[Shaojin Wen]

Some DirectCodeBuilder related optimizations to improve startup and running performance:
1. Merge calls, merge writeU1 and writeU2 into writeU3
2. Merge calls, merge writeU1 and writeIndex operations
3. Directly use writeU1 instead of writeBytecode
4. Rewrite the implementation of load and store

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Commit messages:
 - remove DirectCodeBuilder::writeLocalVar
 - optimize DirectCodeBuilder

Changes: https://git.openjdk.org/jdk/pull/21243/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341141
  Stats: 489 lines in 6 files changed: 297 ins; 35 del; 157 mod
  Patch: https://git.openjdk.org/jdk/pull/21243.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21243/head:pull/21243

PR: https://git.openjdk.org/jdk/pull/21243