RFR: 8292564: x86: Remove redundant casts in Assembler usages

[Vladimir Ivanov]

Clean up Assembler API and remove redundant at use sites.
 
They are not needed anymore because implicit casts between Register and integrals are forbidden now.

Some of the casts are turned into `static_cast`s to assert that constants are small enough to fit into 32-bit immediate.

Testing: hs-tier1 - hs-tier4

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Commit messages:
 - Merge branch 'master' into cast.cleanup
 - CardTable
 - Initial

Changes: https://git.openjdk.org/jdk/pull/9909/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9909&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292564
  Stats: 167 lines in 23 files changed: 0 ins; 35 del; 132 mod
  Patch: https://git.openjdk.org/jdk/pull/9909.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9909/head:pull/9909

PR: https://git.openjdk.org/jdk/pull/9909