RFR: 8368261: Serial: Use more precise nmethod scope during Full GC marking [v3]

[Albert Mingkun Yang]

> Small patch of extracting out the nmethod-marking-scope logic in Serial full-gc. The new `NMethodMarkingScope` is placed in `nmethod.hpp` like its counterpart `ThreadsClaimTokenScope`.
> 
> The new `struct` is almost identical to the existing `MarkScope`, so there is a planned followup PR that will address all other users of `StrongRootsScope` to use the recently introduced `ThreadsClaimTokenScope` and the new `NMethodMarkingScope` introduced in this PR, which would make it less abtract than the name `StrongRootsScope`.
> 
> Test: tier1-3

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27423/files
  - new: https://git.openjdk.org/jdk/pull/27423/files/bd641747..599c5049

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27423&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27423&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27423.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27423/head:pull/27423

PR: https://git.openjdk.org/jdk/pull/27423