RFR: 8133873: Simplify {Register, Unregister}NMethodOopClosure [v2]

[Albert Mingkun Yang]

> Simple change of excluding compressed oops in nmethod closures.

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

  restore assert

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4632/files
  - new: https://git.openjdk.java.net/jdk/pull/4632/files/567bcc4a..3a3b3567

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4632&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4632&range=00-01

  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4632.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4632/head:pull/4632

PR: https://git.openjdk.java.net/jdk/pull/4632