RFR: 8174222: LambdaMetafactory: validate inputs and improve documentation [v2]

[Dan Smith]

> Standardizes and better specifies the errors thrown by LambdaMetafactory, including for inputs that would not be generated by javac.
> 
> Does some renaming of core parameters/fields to better reflect their purpose.
> 
> In the implementation, stops using ACC_BRIDGE for any methods, which is not a good fit for what these methods do (they don't delegate to each other, but all invoke the same implementation method).

Dan Smith has updated the pull request incrementally with one additional commit since the last revision:

  Fix accidentally commented-out parts of test

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4346/files
  - new: https://git.openjdk.java.net/jdk/pull/4346/files/81db8e5e..4b8d0dab

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4346&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4346&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4346.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4346/head:pull/4346

PR: https://git.openjdk.java.net/jdk/pull/4346