Make many functions const

The point is to set up repeated components or boilerplate before their
use sites.

The majority of these make sense as `const`. However, some functions
such as those regarding state may not make sense as `const`.

wgpu/src/renderer.rs

@@ -35,7 +35,7 @@ struct Layer<'a> {
 }
 
 impl<'a> Layer<'a> {
-    pub fn new(bounds: Rectangle<u32>, offset: Vector<u32>) -> Self {
+    pub const fn new(bounds: Rectangle<u32>, offset: Vector<u32>) -> Self {
         Self {
             bounds,
             offset,