RFR: 8341141: Optimize DirectCodeBuilder [v5]

[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 one additional commit since the last revision:

  suggestion from @cl4es and @liach

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21243/files
  - new: https://git.openjdk.org/jdk/pull/21243/files/dab40af9..2ca81a37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=03-04

  Stats: 24 lines in 3 files changed: 0 ins; 0 del; 24 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