RFR: 8332327: Return _methods_jmethod_ids field back in VMStructs

[Andrei Pangin]

The fix for [JDK-8313332](https://bugs.openjdk.org/browse/JDK-8313332) has [removed](https://github.com/openjdk/jdk/commit/21867c929a2f2c961148f2cd1e79d672ac278d27#diff-7d448441e80a0b784429d5d8aee343fcb131c224b8ec7bc70ea636f78d561ecd
) `InstanceKlass::_methods_jmethod_ids` field from VMStructs.

This broke [async-profiler](https://github.com/async-profiler/async-profiler/), since the profiler needs this field to obtain jmethodID in some corner cases.

There was no actual need for removal, as the field is still there in InstanceKlass. So, I propose to return the field back to restore the broken functionality of async-profiler. This is a no risk change, because it only exports an offset of one field and does not affect the JVM otherwise.

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Commit messages:
 - JDK-8332327: Return _methods_jmethod_ids field back in VMStructs

Changes: https://git.openjdk.org/jdk/pull/19254/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19254&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332327
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19254.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19254/head:pull/19254

PR: https://git.openjdk.org/jdk/pull/19254