Remove redundant number conversion in window resolution (#20582)

# Objective

`WindowResolution` stores the width and height as `u32`, but the
constructors take `f32` and just convert straight to `u32`.
Additionally, everywhere in Bevy where a `WindowResolution` is
constructed specifies whole numbers, making the use of a float entirely
pointless.

## Solution

Replace the `f32` constructors with `u32` constructors.

I also decided to change the generic `I: Into<f32>` tuple and array
constructors to only take u32 instead of `I: Into<u32>` for UX reasons.
It allows formatting those constructors as `(1920, 1080).into()`, as the
compiler can infer that the numbers are u32. Keeping those impls generic
prevents that inference, and because the default number type (i32)
doesn't impl `Into<u32>`, that would require formatting it explicitly as
`(1920u32, 1080u32).into()` to compile.

In practice, these generic constructors were only used with whole-number
f32 values anyway, like everything else, so them being generic wasn't
actually leveraged anywhere.

## Testing

Chased type errors until they were all gone