Add Proc#refined(mod1, ...), which returns a new Proc whose body runs
with the given modules' refinements active. The receiver is unchanged
and the captured closure environment is shared; only the refinement
scope differs.

In JRuby whether a call resolves refinements is decided at IR build
time: CallInstr.create reads scope.maybeUsingRefinements() and, when
true, builds a RefinedCachingCallSite that captures the static scope.
So a refinement-aware copy of the receiver proc's IR is required (the
analog of CRuby recursively deep-copying the block iseq); merely
swapping an overlay at runtime is not enough.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Implement Proc#refined

Officially removed for Ruby 4.1.

See https://bugs.ruby-lang.org/issues/22135

Implementation-agnostic behavior is covered by
spec/ruby/core/proc/refined_spec.rb (synced from ruby/spec) and by
CRuby's test/ruby/test_proc.rb (synced as test/mri), so keep only the
tests tied to JRuby internals: clone retention in the IR lexical
parent, JIT compilation of the clone, concurrent refine/refined,
backtrace construction through a top-level clone, and GC survival.

Requested in #9486

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Remove deprecated ObjectSpace#_id2ref

Reduce Proc#refined tests to JRuby-specific ones

The ruby2_keywords method will be deprecated for removal in CRuby
starting with 4.1, with removal currently planned in Ruby 4.5. We
duplicate the documentation change here in preparation for that
process.