RFR: 8292275: javac does not emit SYNTHETIC and MANDATED flags for parameters by default [v5]

[Hannes Greule]

> With this change, javac emits the MethodParameters attribute in cases where the JLS requires the information about synthetic and mandated parameters to be stored (see issue).
> Parameter names are *not* emitted unless the `-parameter` flag is set.
> 
> The relevant changes are in `ClassWriter`, where we go through the params to see if we need the attribute if the `-parameter` flag is not set (if it is set, both names and flags will be emitted).
> For records, the mandated flag wasn't set at all, this is solved by the one line fix in `JavacParser`.
> 
> The changes to `CreateSymbols` and `ClassReader` are needed as they weren't able to deal with missing names in the attribute.
> I also had to update some tests as they got a new constant pool entry.
> 
> Only the mandated flag is covered by tests at the moment, as the occurrences are well-specified in the JLS.
> Please let me know if you want tests for specific appearances of synthetic parameters.

Hannes Greule has updated the pull request incrementally with one additional commit since the last revision:

  address comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9862/files
  - new: https://git.openjdk.org/jdk/pull/9862/files/ebb09f8d..883a2dc1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9862&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9862&range=03-04

  Stats: 64 lines in 2 files changed: 17 ins; 36 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/9862.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9862/head:pull/9862

PR: https://git.openjdk.org/jdk/pull/9862