RFR: 8341141: Optimize DirectCodeBuilder [v25]

[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 four additional commits since the last revision:

 - Fold opcode.bytecode() in writeLoadConstant
 - A few missed places, U1U2U2 seem common enough too to be included
 - Rename writeUtfEntry
 - Fold TAG_UTF8 write into writeUTF

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21243/files
  - new: https://git.openjdk.org/jdk/pull/21243/files/c6e4114c..cd597a2a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=24
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=23-24

  Stats: 43 lines in 4 files changed: 14 ins; 12 del; 17 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