RFR: JDK-8273194: Document the two possible cases when Lookup::ensureInitialized returns [v2]

[Mandy Chung]

> Improve the specification to document the cases when `Lookup::ensureInitialized` returns as specified JVMS 5.5 and matches the implementation.
> 
> Please also review CSR: https://bugs.openjdk.java.net/browse/JDK-8273253

Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:

  review comment

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5343/files
  - new: https://git.openjdk.java.net/jdk/pull/5343/files/3a2aa6da..3f7e66b0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5343&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5343&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5343.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5343/head:pull/5343

PR: https://git.openjdk.java.net/jdk/pull/5343