Implement input hints based on the active tool state (#388)

* Hook up user input hints to display in the frontend status bar

Closes #171

* MVP hint system based on tool FSM

* Fix hints for Fill and Eyedropper tools

* Add icons for keyboard shortcuts

* Fix hints for Pen Tool

* Cleanup

editor/src/input/keyboard.rs

@@ -16,6 +16,7 @@ pub type KeyStates = BitVector<KEY_MASK_STORAGE_LENGTH>;
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 pub enum Key {
 	UnknownKey,
+
 	// MouseKeys
 	Lmb,
 	Rmb,
@@ -87,6 +88,20 @@ pub enum Key {
 	NumKeys,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum MouseMotion {
+	None,
+	Lmb,
+	Rmb,
+	Mmb,
+	ScrollUp,
+	ScrollDown,
+	Drag,
+	LmbDrag,
+	RmbDrag,
+	MmbDrag,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct BitVector<const LENGTH: usize>([StorageType; LENGTH]);