RFR: 8328998: Encoding support for Intel APX extended general-purpose registers

[Steve Dohrmann]

Add instruction encoding support for Intel APX extended general-purpose registers:

Intel Advanced Performance Extensions (APX) doubles the number of general-purpose registers, from 16 to 32. For more information about APX, see https://www.intel.com/content/www/us/en/developer/articles/technical/advanced-performance-extensions-apx.html.

By specification, instruction encoding remains unchanged for instructions using only the lower 16 GPRs. For cases where one or more instruction operands reference extended GPRs (Egprs), encoding targets either REX2, an extension of REX encoding, or an extended version of EVEX encoding. These new encoding schemes extend or modify existing instruction prefixes only when Egprs are used.

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Commit messages:
 - fix 32-bit build prefix functions
 - - add UseAPX x86 global
 - add signature for 32-bit build
 - - inlcude previous WREX2 bug fix
 - Merge branch 'master' into apx-encoding-pr
 - Instruction encoding support for APX extended GPRs -- initial commit

Changes: https://git.openjdk.org/jdk/pull/18476/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18476&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328998
  Stats: 859 lines in 4 files changed: 424 ins; 36 del; 399 mod
  Patch: https://git.openjdk.org/jdk/pull/18476.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18476/head:pull/18476

PR: https://git.openjdk.org/jdk/pull/18476