RFR: 8311847: Fix -Wconversion for assembler.hpp emit_int8,16 callers [v3]

[Coleen Phillimore]

> Please review changes to fix -Wconversion warnings that come from assembler_<cpu>.cpp by adding narrow_casts to the emit_int8,16,24, and 32 functions.  And some other fixups with checked_cast.
> 
> Ran tier1 on Oracle platforms, and tier1-4 on linux-x64-debug, linux-aarch64-debug, windows-x64-debug.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Unset Wconversion

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14822/files
  - new: https://git.openjdk.org/jdk/pull/14822/files/12b1e95b..71c8fdec

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14822&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14822&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14822.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14822/head:pull/14822

PR: https://git.openjdk.org/jdk/pull/14822