egui_glow: Add function to set the texture filter (#1041)

* Allow setting the scale filter for `glow` backend

This commit adds a `set_scale_filter` method to the `glow` painter so that
textures can be set to scale using nearest-neighbour scaling rather than
linear. This is useful for pixel art.

I wasn't entirely sure what kind of API you want for this kind of change so I
went with what seemed least intrusive, I don't mind doing something more
holistic if this isn't what you had in mind.

* Rename scale_filter -> texture_filter

* Store the TextureFilter directly

* PR link in changelog

* Use inter-doc links

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

egui_glow/src/misc_util.rs

@@ -2,10 +2,13 @@
 use glow::HasContext;
 use std::option::Option::Some;
 
+use crate::painter::TextureFilter;
+
 pub(crate) fn srgbtexture2d(
     gl: &glow::Context,
     is_webgl_1: bool,
     srgb_support: bool,
+    texture_filter: TextureFilter,
     data: &[u8],
     w: usize,
     h: usize,
@@ -20,12 +23,12 @@ pub(crate) fn srgbtexture2d(
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,
             glow::TEXTURE_MAG_FILTER,
-            glow::LINEAR as i32,
+            texture_filter.glow_code() as i32,
         );
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,
             glow::TEXTURE_MIN_FILTER,
-            glow::LINEAR as i32,
+            texture_filter.glow_code() as i32,
         );
         gl.tex_parameter_i32(
             glow::TEXTURE_2D,