Fix Hamcrest not() unwrap infinite loop and support CoreMatchers

[Jammy-Louie]

What's changed

Two commits:

1. Fix an infinite loop in HamcrestMatcherToJUnit5 / HamcrestInstanceOfToJUnit5 on a not(...) matcher that isn't org.hamcrest.Matchers.not.
2. Migrate CoreMatchers variants of not/instanceOf/isA instead of skipping them.

The hang

The unwrap loop continues on a name check but only makes progress on a type check, so they disagree:

while ("not".equals(matcherInvocation.getSimpleName())) {          // any not
    matcherInvocation = new RemoveNotMatcherVisitor().visit(...);  // only strips org.hamcrest.Matchers.not
}

A CoreMatchers.not (or a not with unresolved type) never gets stripped, the name stays "not", and the loop spins forever. Repro:

import static org.hamcrest.CoreMatchers.not;
import static org.hamcrest.CoreMatchers.equalTo;
assertThat(a, not(equalTo(b))); // hangs

Fix: loop on the matcher that decides strippability, so continuation and progress can't disagree:

while (RemoveNotMatcherVisitor.NOT_MATCHER.matches(matcherInvocation)) {

No change to existing migrations.

CoreMatchers support

Broadens the three matchers from org.hamcrest.Matchers to org.hamcrest.*Matchers (matches exactly Matchers and CoreMatchers, identical methods), so CoreMatchers.not/instanceOf/isA migrate too.

Tests

notFromCoreMatchers (both recipes, asserting the real migration, @Timeout-guarded so a regressed hang fails fast) and instanceOfAndIsAFromCoreMatchers. Full suite passes.

[timtebeek]

Perfect, thanks a lot! This explains why I was seeing timeouts with AssertJ indeed.