merge revision(s) fb4cf204,fa0279d9: [Backport #17725]

	use me->def instead of me for opt_table

	`vm_opt_method_table` is me=>bop table to manage the optimized
	methods (by specialized instruction). However, `me` can be invalidated
	to invalidate the method cache entry.
	[Bug #17725]

	To solve the issue, use `me-def` instead of `me` which simply copied
	at invalidation timing.

	A test by @jeremyevans https://github.com/ruby/ruby/pull/4376
	---
	 test/ruby/test_method.rb | 15 +++++++++++++++
	 vm.c                     | 11 +++++------
	 2 files changed, 20 insertions(+), 6 deletions(-)

	should not share same `def` for specialized method

	Because the key of redefine table is `def`, `def` should be
	unique for each optimized method (`alias` is not allowed).
	---
	 array.c | 2 +-
	 1 file changed, 1 insertion(+), 1 deletion(-)