RFR: 8343188: Investigate ways to simplify MemorySegment::ofBuffer

[Per Minborg]

This PR proposes to improve `MemorySegment::ofBuffer` making it more amenable to inlining and generally improving performance.

Testing successfully on tier1-3

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Commit messages:
 - Remove switch rake and move factories to Buffer impls
 - Clean up generated code
 - Revert changes
 - Remove unused imports
 - Move scale factor into Buffer implementations
 - Refactor AMSI::ofBuffer

Changes: https://git.openjdk.org/jdk/pull/21764/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21764&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343188
  Stats: 282 lines in 9 files changed: 220 ins; 48 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/21764.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21764/head:pull/21764

PR: https://git.openjdk.org/jdk/pull/21764