Add cast_lossless lints for char to uint, small int to usize/isize, and float casts

[TanmayArya-1p]

Closes #14469

changelog: [cast_lossless]: new lints on char to uint casts (u32/u64/u128), small ints (<=16 bits) to usize/isize and smaller floats to f128(if available). Also improves macro handling.

[rustbot]

r? @samueltardieu

rustbot has assigned @samueltardieu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[github-actions]

Lintcheck changes for b9024f3

Lint	Added	Removed	Changed
clippy::cast_lossless	533	0	154

This comment will be updated if you push new changes

[TanmayArya-1p]

I have tried to address the issues pointed out in #14470. Particularly, I've implemented @Jarcho's suggestion using walk_span_to_context for proper macro hygiene check. Also, the type checking logic is derived from this comment.