Refactor various operator[] based on BETA10 (#1110)

* Tidy up `operator[]` code

* Add weird index operator for `FUN_1002ddc0`

* Cleanup

* Add Matrix4 BETA10 annotations, fix typo

---------

Co-authored-by: jonschz <jonschz@users.noreply.github.com>

LEGO1/realtime/vector.h

@@ -163,14 +163,6 @@ public:
 		return *this;
 	}
 
-	// There is another candidate for `Vector2::operator[]` at BETA10 0x10010890, which is called from only three
-	// functions in BETA10:
-	// - `Matrix4::FromQuaternion()`
-	// - `Matrix4::ToQuaternion()`
-	// - `UnknownMx4DPointFloat::FUN_100040a0()`
-	// Maybe there is another subclass of `Vector4` involved that has the same VTABLE but a different `operator[]`.
-	// It is also interesting that `Matrix4::operator[]` is located right above at BETA10 0x10010860.
-
 	// FUNCTION: BETA10 0x1001d140
 	float& operator[](int idx) { return m_data[idx]; }
 
@@ -416,6 +408,11 @@ public:
 		m_data[3] = p_value;
 	} // vtable+0x84
 
+	float& operator[](int idx) { return m_data[idx]; }
+
+	// FUNCTION: BETA10 0x10010890
+	const float& operator[](int idx) const { return m_data[idx]; }
+
 	friend class Mx4DPointFloat;
 };