[ruby-core:116523] [Ruby master Bug#20230] Fix crash when passing large keyword splat to method accepting keywords and keyword splat

Issue #20230 has been reported by jeremyevans0 (Jeremy Evans).

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Bug #20230: Fix crash when passing large keyword splat to method accepting keywords and keyword splat
https://bugs.ruby-lang.org/issues/20230

* Author: jeremyevans0 (Jeremy Evans)
* Status: Open
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
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The following code causes a crash in Ruby 2.2-3.3 and master:

```ruby
h = {}
1000000.times{|i| h[i.to_s.to_sym] = i}
def f(kw: 1, **kws) end
f(**h)
```

Inside a thread or fiber, the size of the keyword splat could be much smaller and still cause a crash.  This is similar to the issue in #4040, but for keyword splats instead of positional splats.

I found this issue while optimizing method calling by reducing implicit allocations. Given the following code:

```ruby
def f(kw: , **kws) end
kw = {kw: 1}
f(**kw)
```

The `f(**kw)` call previously allocated two hashes callee side instead of a single hash. This is because `setup_parameters_complex` would extract the keywords from the keyword splat hash to the C stack, to attempt to mirror the case when literal keywords are passed without a keyword splat. Then, `make_rest_kw_hash` would build a new hash based on the extracted keywords that weren't used for literal keywords.

I have submitted a pull request which changes the implementation so that if a keyword splat is passed, literal keywords are deleted from the keyword splat hash (or a copy of the hash if the hash is not mutable): https://github.com/ruby/ruby/pull/9776

In addition to fixing the bug, the new implementation also eliminates the unnecessary hash allocation.



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