[Bug #21186] multibyte char literal should be a single letter word

[Bug #20668]

The `dest` node is assumed to be a `CDECL`, so overwriting it with
a `LIT` cause a crash on the next iteration.

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

	[Bug #20521] ripper: Clean up strterm

[Bug #20280]

Backport of #10014.

	[Bug #20517] Make a multibyte character one token at meta escape

	[Bug #20094] Distinguish `begin` and parentheses

merge revision(s) 596db9c1f486d6609a4e97d82c8c71b54609fb6f: [Backport #20090]

	[Feature #19370] Blocks without anonymous parameters should not
	 affect

	---
	 parse.y                  | 4 ++--
	 test/ruby/test_syntax.rb | 7 +++++++
	 2 files changed, 9 insertions(+), 2 deletions(-)

	Use index for referring to symbols in `args` rule instead of named
	 references

	In `args: args ',' arg_splat`, `args` is not unique name.
	Currently the associated rule is interpreted as
	`$$ = rest_arg_append(p, $$, $3, &@$);`.
	The action works as expected because `$$` is initialized with
	`$1` before each action is executed.
	However it's misleading then change to use index.
	---
	 parse.y | 4 ++--
	 1 file changed, 2 insertions(+), 2 deletions(-)

This reverts commit d4b780e84e9a6b858d0f6c6a44b22da0d2f5835e.

	[Bug #20094] Distinguish `begin` and parentheses

	---
	 compile.c                    |  1 +
	 parse.y                      | 36 +++++++++++++++++++++---------------
	 test/ruby/test_whileuntil.rb | 18 ++++++++++++++++++
	 3 files changed, 40 insertions(+), 15 deletions(-)