[Bug #19619] Preserve numbered parameters context

	Preserve numbered parameters context across method definitions

	[Bug #20468] Fix safe navigation in `for` variable

[Bug #20180]

Backports #9624.

This reverts commit 24dd529750c08b5603fb418a4f34998b9bf6c8f9.

	[Bug #19973] Warn duplicated keyword arguments after keyword splat

	---
	 parse.y                  | 11 +++++++----
	 test/ruby/test_syntax.rb |  6 ++++++
	 2 files changed, 13 insertions(+), 4 deletions(-)

	Add tests for `return` in `BEGIN` and `END` blocks

	---
	 spec/ruby/language/return_spec.rb | 15 +++++++++++++++
	 test/ruby/test_syntax.rb          |  1 +
	 2 files changed, 16 insertions(+)

	[Bug #19774] Fix segfault at `return` in `END`

	---
	 eval_error.c             | 7 ++++++-
	 test/ruby/test_syntax.rb | 5 +++++
	 2 files changed, 11 insertions(+), 1 deletion(-)

	[Bug #19025] Numbered parameter names are always local variables

	---
	 parse.y                  | 2 +-
	 test/ruby/test_syntax.rb | 1 +
	 2 files changed, 2 insertions(+), 1 deletion(-)

[Feature #19134]

https://bugs.ruby-lang.org/issues/19134?next_issue_id=19133&prev_issue_id=19135#note-4

[Feature #19134]