[ruby-core:107302] [Ruby master Bug#18553] Memory leak on compiling method call with kwargs

Issue #18553 has been reported by ibylich (Ilya Bylich).

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Bug #18553: Memory leak on compiling method call with kwargs
https://bugs.ruby-lang.org/issues/18553

* Author: ibylich (Ilya Bylich)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
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The following code produces a memory leak:

```ruby
p(foo: 1)
```

It comes from the allocation in `compile.c`:

```c
struct rb_callinfo_kwarg *kw_arg =
                rb_xmalloc_mul_add(len, sizeof(VALUE), sizeof(struct rb_callinfo_kwarg));
```

Later it's packed into `struct rb_callinfo`, but `imemo_callinfo` is a GC-managed object that has no `free` calls in `obj_free` function in gc.c.

[I've tried to fix it](https://github.com/ruby/ruby/pull/5488/files#diff-d1cee85c3b0e24a64519c11150abe26fd0b5d8628a23d356dd0b535ac4595d49R3397) by calling `free` on `callinfo->kwarg` and it fixed leak in `./miniruby -e 'p(foo: 1)'`, but it breaks `make install`. My addition causes a double-free error, looks like either `callinfo` or `callinfo->kwarg` is shared between multiple objects. 
`kwarg` field is a `const` pointer, so that's somewhat expected (I was under impression that `const` qualifier is redundant) :)

I'm pretty sure old versions of Ruby are also affected by this memory leak.



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