ui: build paths as ops

Instead of allocating and constructing a clip path, store path data
directly in op lists. Use separate op lists for cached text layout
paths.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/internal/path/path.go

@@ -4,15 +4,8 @@ package path
 
 import (
 	"unsafe"
-
-	"gioui.org/ui/f32"
 )
 
-type Path struct {
-	Vertices []Vertex
-	Bounds   f32.Rectangle
-}
-
 // The vertex data suitable for passing to vertex programs.
 type Vertex struct {
 	CornerX, CornerY int16