LibWeb/SVG: Move path data into Path.{h,cpp}

More things need this than just the `<path>` element, so let's avoid
having to include `SVGPathElement.h` in places that don't need it.

Minor changes at the same time:
- Wrap it in a Path class
- Specify underlying type for PathInstructionType
- Make a couple of free functions into methods
- Give PathInstruction an operator==

No functionality changes.

Libraries/LibWeb/SVG/SVGPathElement.h

@@ -6,9 +6,7 @@
 
 #pragma once
 
-#include <LibGfx/Bitmap.h>
-#include <LibWeb/HTML/HTMLElement.h>
-#include <LibWeb/SVG/AttributeParser.h>
+#include <LibWeb/SVG/Path.h>
 #include <LibWeb/SVG/SVGGeometryElement.h>
 
 namespace Web::SVG {
@@ -29,9 +27,7 @@ private:
 
     virtual void initialize(JS::Realm&) override;
 
-    Vector<PathInstruction> m_instructions;
+    Path m_path {};
 };
 
-[[nodiscard]] Gfx::Path path_from_path_instructions(ReadonlySpan<PathInstruction>);
-
 }