RFR: 8323779: Serial: Remove Generation::promotion_attempt_is_safe [v2]

[Albert Mingkun Yang]

> Simple updating a field type to use more concrete type.

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/17439/files
  - new: https://git.openjdk.org/jdk/pull/17439/files/36e85243..2a0318e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17439&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17439&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17439.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17439/head:pull/17439

PR: https://git.openjdk.org/jdk/pull/17439