fix(ext/ffi): Use c_char instead of i8 in op_ffi_cstr_read for compatibility with aarch64

[LukeChannings]

👋

This patch fixes a build error I get when compiling for aarch64 in Linux:

Compiling deno_ffi v0.16.0 (/deno/ext/ffi)
error[E0308]: mismatched types
   --> ext/ffi/lib.rs:612:30
    |
612 |   Ok(unsafe { CStr::from_ptr(ptr) }.to_str()?.to_string())
    |                              ^^^ expected `u8`, found `i8`
    |
    = note: expected raw pointer `*const u8`
               found raw pointer `*const i8`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `deno_ffi` due to previous error
warning: build failed, waiting for other jobs to finish...
error: build failed

This is caused by CStr::from_ptr returning an i8 on aarch64, instead of a u8.
Using std::os::raw::c_char will handle the underlying type differences (I think).

I've compiled with this patch here and it compiles correctly for aarch64.

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[crowlKats]

CI is failing due to bad formatting, could you please run tools/format.js?

[LukeChannings]

@crowlKats Sorry about that, it passes formatting / linting locally now and I've pushed an update.

[crowlKats]

LGTM

[LukeChannings]

cc. @eliassjogreen since this is his code.

[eliassjogreen]

LGTM