Shaders: add gcore-shaders and make graster-nodes no-std (#2925)

* gcore-shaders: add crate, move `color` and `blending` from gcore

* gcore-shaders: move `AsU32`

* gcore-shaders: move `ChoiceType`, switch `Cow` for `&str`, adjust node macro

* gcore-shaders: move `registry::types`

* gcore-shaders: move `context::Ctx`

* raster-nodes: make it `no_std` with `std` feature

* gcore-shaders: fix doctest

node-graph/gcore-shaders/src/lib.rs

@@ -0,0 +1,17 @@
+pub mod blending;
+pub mod choice_type;
+pub mod color;
+pub mod context;
+pub mod registry;
+
+pub use context::Ctx;
+pub use glam;
+
+pub trait AsU32 {
+	fn as_u32(&self) -> u32;
+}
+impl AsU32 for u32 {
+	fn as_u32(&self) -> u32 {
+		*self
+	}
+}