[validation] Parse sources with Rewrite slower than JDT

[BoykoAlex]

Investigate possible performance improvements in parsing CUs with Rewrite as they seem slower than with JDT.
This is important to reconcile code in the opened editor while user is typing.

[BoykoAlex]

STS4 side: ac946ff (RewriteCompilationUnitCache has JavaParser#reset(Collection<URI>) call commented out until PR is merged into Rewrite)
Rewrite commits:
openrewrite/rewrite@45f828b
Rewrite PRs:
openrewrite/rewrite#2789
openrewrite/rewrite#2821

[BoykoAlex]

Rewrite PRs merged. Our side integration of changes from Rewrite: 18c4c10