Java Editor: remove some reflective calls and improve logging

[mbien]

VanillaPartialParser:

• partial reparse verification is now controlled by the log level
  (-J-Dorg.netbeans.modules.java.source.parsing.VanillaPartialReparser.level=FINE)
• improved logging (e.g formatting for easy comparison)
• removed some reflective calls

Tiny, JavaCompletionItem:

• some enums can be now used directly

GeneratorUtilities, ClipboardHandler:

• remove remaining string template code from Make NetBeans aware of the StringTemplate.STR default field import. #6908
• minor cleanup

[eirikbakke]

I'm not super-familiar with this area, but the cleanups all made sense when reading through them line by line and comparing with the PR description.

[mbien]

to give more context: while working on one of the hint performance improvement PRs, I noticed that essentially everything ran twice, so I searched for the cause and saw this after tweaking log levels:

WARNING [org.netbeans.modules.java.source.parsing.VanillaPartialReparser]: Incorrect partial reparse detected, dump filed ...

(I do also have a small reproducer for this but haven't investigated beyond that)

This would only happen with -ea enabled. So I improved the log output a bit and made that verification step log level dependent instead of based on assertions - so that it can be more selectively switched on/off without more side effects.

To make it worth a PR I also added reflection removal from my stash which was in the same file and similar cases in related files which fit the theme.

[mbien]

rebased, going to merge once green. thanks for review!