Ref #5597

Avoid losing the upper digits for mruby binary

The function may invoke the garbage collection and it requires
`mrb_state` to run.

- `rlen` keeps 16 bits.
- `ilen` keeps 32 bits.

Note that this change will break mruby binary format compatibility.

With some refactoring.

* `ret` argument is always non-nil, so no check needed.
* move allocation check right after malloc().
* simplify conditions.

The existence of this member reduces memory and execution time.

Add `Array#{repeated_combination,repeated_permutation}` methods

Ruby 1.9.2 feature.

ref: https://docs.ruby-lang.org/ja/3.1.0/method/Array/i/repeated_combination.html
ref: https://docs.ruby-lang.org/ja/3.1.0/method/Array/i/repeated_permutation.html

fix #5593

It used to return wrong value for 14 positional arguments.

Now `iv_get()` returns `pos+1` if it finds the entry, so you don't need
to call `iv_put()`. You can replace the entry value by assigning to
`t->ptr[pos-1]`.

Class variables are slower than instance variables of classes.

Instead embed deleted flag in the key (`mrb_sym` only occupies 30bits).

`iv_size()` is approximated by the allocated table size.

As a general principles numeric instructions should not be prefixed by
`OP_EXT` instructions since they are not supported by "mruby/c".

This is a fundamentally simplified reimplementation of #5317
by @shuujii

Instead of having array of `struct iv_elem`, we have sequences of keys
and values packed in single chunk of malloc'ed memory. We don't have to
worry about gaps from alignment, especially on 64 bit architecture,
where `sizeof(struct iv_elem)` probably consumes 16 bytes, but
`sizeof(mrb_sym)+sizeof(mrb_value)` is 12 bytes.

In addition, this change could improve memory access locality.

close #5317

Align "wrong number of arguments" messages

Fixed compile error for `mrbgems/mruby-cmath` with `clang++`

Fix `args_unshift()` in `mrbgems/mruby-method`

Make "N for M" into the form "given N, expected M".

As I worked, I noticed that the `argnum_error()` function had a part to include the method name in the message.
I think this part is no longer needed by https://github.com/mruby/mruby/pull/5394.

  - Before this patch

    ```console
    % bin/mruby -e '[1, 2, 3].each 0'
    trace (most recent call last):
            [1] -e:1
    -e:1:in each: 'each': wrong number of arguments (1 for 0) (ArgumentError)
    ```

  - After this patch

    ```console
    % bin/mruby -e '[1, 2, 3].each 0'
    trace (most recent call last):
            [1] -e:1
    -e:1:in each: wrong number of arguments (given 1, expected 0) (ArgumentError)
    ```

If the preprocessor check part is only `__clang__`, CI's such as `Ubuntu-2004-clang` will fail to compile.
This is why we limited the addition to FreeBSD and OpenBSD, which have `clang++` in their base systems.
DragonFly BSD and NetBSD have GCC built into their base systems, so nothing is changed.

Both keyword arguments and block arguments were being destroyed when there were no arguments.
The cause of this is #5585. I' m sorry.