RFR: 7903321: Use a set instead of a map to record methods in class 'MethodGroup' [v3]

[Guoxiong Li]

> Hi all,
> 
> This patch changes the type of the field `MethodGroup#methods` from a map to a set so that it is more suitable for its meaning.
> 
> Thanks for the taking the time to review.
> 
> Best Regards,
> -- Guoxiong

Guoxiong Li has updated the pull request incrementally with one additional commit since the last revision:

  Fix exception message.

-------------

Changes:
  - all: https://git.openjdk.org/jmh/pull/79/files
  - new: https://git.openjdk.org/jmh/pull/79/files/e585e859..52960cc8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmh&pr=79&range=02
 - incr: https://webrevs.openjdk.org/?repo=jmh&pr=79&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmh/pull/79.diff
  Fetch: git fetch https://git.openjdk.org/jmh pull/79/head:pull/79

PR: https://git.openjdk.org/jmh/pull/79