RFR: 8343140: JfrJavaSupport uses the wrong accessors for sub-int fields [v2]

[Daniel Jeliński]

> This test fixes the accessor used by `read_boolean_field` to access boolean fields of the `jdk.jfr.internal.dcmd.Argument` record. It also fixes the read accessors for `short` and `char` types, and marks the write accessors for `boolean`, `short` and `char` as unimplemented.
> 
> The existing accessor reads the boolean field as int. This results in unaligned access, and probably reads incorrect value on big-endian CPUs.
> 
> No new tests. I'm sure a test would be useful, but I have no idea how to write one. Existing tier1-3 tests continue to pass.

Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:

  Implement write accessors

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21952/files
  - new: https://git.openjdk.org/jdk/pull/21952/files/ea1a0062..639e57d9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21952&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21952&range=00-01

  Stats: 23 lines in 1 file changed: 22 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21952.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21952/head:pull/21952

PR: https://git.openjdk.org/jdk/pull/21952