RFR: 8351162: Clean up x86 (Macro)Assembler after 32-bit x86 removal

[Aleksey Shipilev]

This improvement targets x86 `(Macro)Assembler`. We are mostly cleaning up `LP64` predicated code blocks, and a bit of related code.

It is enticing to remove all `*ptr` methods, and rename all uses from `*ptr` to `*q`, but that turns out to be very intrusive. That is left for a future RFE, if we ever consider doing it.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `all`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/24631/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24631&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351162
  Stats: 1394 lines in 6 files changed: 2 ins; 1253 del; 139 mod
  Patch: https://git.openjdk.org/jdk/pull/24631.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24631/head:pull/24631

PR: https://git.openjdk.org/jdk/pull/24631