RFR: 8322294: Cleanup NativePostCallNop

[Richard Reingruber]

This is a refactoring/cleanup of `NativePostCallNop` that simplifies the ppc64 port.

* `frame::get_oop_map()` is moved to shared code

* encoding / decoding details of the oopmap slot and the CodeBlob offset are moved from shared code to the platform dependent implementations of `bool NativePostCallNop::patch(int32_t oopmap_slot, int32_t cb_offset)` and `bool NativePostCallNop::decode(int32_t& oopmap_slot, int32_t& cb_offset)`

The change passed our CI testing. JTReg tests: tier1-4 of hotspot and jdk. All of Langtools and jaxp. SPECjvm2008, SPECjbb2015, Renaissance Suite, and SAP specific tests.
All testing was done with fastdebug and release builds on the main platforms and also on Linux/PPC64le and AIX.

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Commit messages:
 - 8322294: Cleanup NativePostCallNop

Changes: https://git.openjdk.org/jdk/pull/17150/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17150&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322294
  Stats: 203 lines in 30 files changed: 53 ins; 114 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/17150.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17150/head:pull/17150

PR: https://git.openjdk.org/jdk/pull/17150