RFR: 8261407: ReflectionFactory.checkInitted() is not thread-safe [v7]

[liach]

> Upon review of [8261407](https://bugs.openjdk.java.net/browse/JDK-8261407), by design, duplicate initialization of ReflectionFactory should be safe as it performs side-effect-free property read actions, and the suggesting of making the `initted` field volatile cannot prevent concurrent initialization either; however, having `initted == true` published without the other fields' values is a possibility, which this patch addresses.
> 
> This simulates what's done in `CallSite`'s constructor for `ConstantCallSite`. Please feel free to point out the problems with this patch, as I am relatively inexperienced in this field of fences and there are relatively less available documents. (Thanks to https://shipilev.net/blog/2014/on-the-fence-with-dependencies/)

liach has updated the pull request incrementally with two additional commits since the last revision:

 - The fast path should always come first. good lesson learned!
   restore config field comments
 - Try making the config a record and see if it works

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6889/files
  - new: https://git.openjdk.java.net/jdk/pull/6889/files/f32ff988..affda902

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6889&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6889&range=05-06

  Stats: 55 lines in 1 file changed: 9 ins; 19 del; 27 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6889.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6889/head:pull/6889

PR: https://git.openjdk.java.net/jdk/pull/6889