Add gdb pretty printers for slices types (`&[T]` and `&mut [T]`).

[EFanZh]

Currently, support for pretty-printing slice types is missing for rust-gdb.

[DaviRain-Su]

Can you describe in more detail?

[EFanZh]

rust-gdb provides pretty-printing function for some Rust types, such as &str, Vec, HashMap, etc. This allows gdb to display values of some types in a more readable way. I think it is implemented in the following files:

• https://github.com/rust-lang/rust/blob/master/src/etc/gdb_lookup.py,
• https://github.com/rust-lang/rust/blob/master/src/etc/gdb_providers.py,
• https://github.com/rust-lang/rust/blob/master/src/etc/rust_types.py.

Currently, slices can only be displayed as a pointer and a length value in the debugger. I hope rust-gdb can support displaying slices.

I also noticed that rust-lldb already supports pretty-printing const slices (&[T]), but not mutable slices (&mut [T]). Maybe rust-lldb can also add pretty-printing support fur mutable slices.

[inquisitivecrystal]

@rustbot label A-slice C-enhancement T-dev-tools