RFR: 8341141: Optimize DirectCodeBuilder [v15]

[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

Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:

 - label write clean
 - optimizer for codeSize

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21243/files
  - new: https://git.openjdk.org/jdk/pull/21243/files/77174a2b..36c81ec1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=14
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=13-14

  Stats: 138 lines in 3 files changed: 66 ins; 25 del; 47 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