Support optional number of components on an Image to improve public facing API

[oisyn]

This PR adds a components parameter to the Image type and Image! macro. The value (in range 1..=4) is implied for any specified format other than unknown, and can be explicitely specified when used together with the type argument (when omitted, it defaults to 4, which makes it backwards compatible with old code).

This causes the relevant image sampling functions, such as fetch(), sample(), and read(), to return a scalar or vector with those exact number of dimensions, rather than always a 4d vector.

Example usage:

#[spirv(fragment)]
pub fn main(
    #[spirv(descriptor_set = 0, binding = 0)] image1: &Image!(2D, type=f32, sampled, components=1),
    #[spirv(descriptor_set = 0, binding = 1)] image2: &Image!(2D, type=f32, sampled, components=2),
    #[spirv(descriptor_set = 0, binding = 2)] image3: &Image!(2D, type=f32, sampled, components=3),
    #[spirv(descriptor_set = 0, binding = 3)] image4: &Image!(2D, type=f32, sampled),
    #[spirv(descriptor_set = 0, binding = 4)] image2_implied: &Image!(2D, format=rg16f, sampled),
    #[spirv(descriptor_set = 0, binding = 5)] image3_implied: &Image!(2D, format=r11f_g11f_b10f, sampled),
    output: &mut glam::Vec4,
) {
    let coords = glam::IVec2::new(0, 1);
    let t1 = image1.fetch(coords);         // f32
    let t2 = image2.fetch(coords);         // Vec2
    let t3 = image3.fetch(coords);         // Vec3
    let t4 = image4.fetch(coords);         // Vec4
    let t5 = image2_implied.fetch(coords); // Vec2
    let t6 = image3_implied.fetch(coords); // Vec3
    *output = Vec4::splat(t1) + ((t2 + t5).extend(0.0) + t3 + t6).extend(0.0) + t4;
}