RFR: 8294059: Serial: Refactor GenCollectedHeap::collect [v2]

[Albert Mingkun Yang]

> Simple cleanup of control flow in `GenCollectedHeap::collect`.
> 
> Test: hotspot_gc

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

  Update src/hotspot/share/gc/shared/genCollectedHeap.cpp
  
  Co-authored-by: Stefan Johansson <54407259+kstefanj at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10355/files
  - new: https://git.openjdk.org/jdk/pull/10355/files/0baef977..5f100231

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10355&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10355&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10355.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10355/head:pull/10355

PR: https://git.openjdk.org/jdk/pull/10355