RFR: 8375646: Some parser flags seem unused

[Maurizio Cimadamore]

Some of the flags in `JavacParser` are never set, such as `TYPEARGS` and `NOPARAMS`.

Another flag, namely `NODIAMOND` can easily be avoided by looking ahead one token.

This PR removes all the three flags. The main issue with these changes had to do with removing the `boolean allowDiamon` parameter from the `typeArguments` method, as doing so makes it clash with another similarly named method.
For this reason, this PR distinguish between:

* `typeArguments` -- a method that parses a type argument list, returns a list of `JCExpression`s
* `typeApply` -- a method that parses and applies type arguments to an existing type (a `JCExpression). This returns a new `JCExpression` (typically a `JCTypeApply`).

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Commit messages:
 - Drop leftover comment
 - Initial push

Changes: https://git.openjdk.org/jdk/pull/29302/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29302&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375646
  Stats: 69 lines in 1 file changed: 13 ins; 18 del; 38 mod
  Patch: https://git.openjdk.org/jdk/pull/29302.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29302/head:pull/29302

PR: https://git.openjdk.org/jdk/pull/29302