RFR: 8224980: FLAG_SET_ERGO silently ignores invalid values [v3]

[Ioi Lam]

> Clarify the `FLAG_SET_ERGO` API - the caller must ensure that a valid value is passed. Added an assert to check this.
> 
> Fixed two issues found by the assert:
> 
> - `NonNMethodCodeHeapSize`
> - `XXXThreshold` and `XXXNotifyFreqLog` flags in `CompilerConfig::set_compilation_policy_flags()`

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  @dholmes-ora suggestion

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12549/files
  - new: https://git.openjdk.org/jdk/pull/12549/files/adef377e..8cf4b6e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12549&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12549&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12549.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12549/head:pull/12549

PR: https://git.openjdk.org/jdk/pull/12549