RFR: Update nmethod caching and clean up unused/duplicate methods [v4]

[Ashutosh Mehra]

> This PR updates nmethod caching to be based on caching of CodeBlob. It also cleans up some dead code and duplicate methods.

Ashutosh Mehra has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:

 - Merge 8358330: AsmRemarks and DbgStrings clear() method may not get called before their destructor
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Fix undefs
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Merge branch 'premain' into update-nmethod-caching
 - Remove AOTCodeEntry::_blob_offset
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Remove CodeBuffer::clear_strings() as the relevant destructors clear the
   strings
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Remove redundant call to clear()
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - More cleanup
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Fix compile failures
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Refactor nmethod caching
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Replace apply_relocations with fix_relocations
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>

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Changes: https://git.openjdk.org/leyden/pull/71/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=71&range=03
  Stats: 889 lines in 11 files changed: 179 ins; 584 del; 126 mod
  Patch: https://git.openjdk.org/leyden/pull/71.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/71/head:pull/71

PR: https://git.openjdk.org/leyden/pull/71