RFR: 8341141: Optimize DirectCodeBuilder [v14]

[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:

 - optimize MethodTypeDescImpl::descriptorString
 - Remove redundant requireNonNull

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21243/files
  - new: https://git.openjdk.org/jdk/pull/21243/files/4e1e5daf..77174a2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=13
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21243&range=12-13

  Stats: 30 lines in 3 files changed: 17 ins; 5 del; 8 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