RFR: 8358294: Remove unnecessary GenAlignment [v2]

[Albert Mingkun Yang]

> Simple replacement of `GenAlignment` with `SpaceAlignment`, because they always have the same value. Removing the former to reduce complexity.
> 
> Test: tier1-3

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into remove-gen-alignment
 - remove-gen-alignment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25577/files
  - new: https://git.openjdk.org/jdk/pull/25577/files/987f3d51..d21a02e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25577&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25577&range=00-01

  Stats: 29666 lines in 802 files changed: 23009 ins; 4069 del; 2588 mod
  Patch: https://git.openjdk.org/jdk/pull/25577.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25577/head:pull/25577

PR: https://git.openjdk.org/jdk/pull/25577