gpu: rename resourceCache to textureCache and use concrete key

The only remaining use of the cache is mapping handles to textures.
Using a concrete type for the key avoids the allocation caused by convT.

If we need more caches again in the future we can copy the type, or make
it generic.

Instead of updating the benchmark, we removed it outright. It suffered
from several flaws:

- The amount of work for each iteration of b.N wasn't constant, because
  the same cache was reused, growing ever larger in size.

- It only tested the cost of insertions. The comment "half are the same
  and half updated" wasn't true, as calling 'put' with the same key twice
  would've resulted in a panic.

- It didn't simulate any particular workload or cache size, making the
  benchmark useless for comparing different cache implementations. The
  cost of insertions isn't particularly interesting.

Signed-off-by: Dominik Honnef <dominik@honnef.co>

gpu/gpu.go

@@ -51,7 +51,7 @@ type GPU interface {
 }
 
 type gpu struct {
-	cache *resourceCache
+	cache *textureCache
 
 	profile                                string
 	timers                                 *timers
@@ -359,7 +359,7 @@ func NewWithDevice(d driver.Device) (GPU, error) {
 
 func newGPU(ctx driver.Device) (*gpu, error) {
 	g := &gpu{
-		cache: newResourceCache(),
+		cache: newTextureCache(),
 	}
 	g.drawOps.pathCache = newOpCache()
 	if err := g.init(ctx); err != nil {
@@ -460,12 +460,8 @@ func (g *gpu) Profile() string {
 	return g.profile
 }
 
-func (r *renderer) texHandle(cache *resourceCache, data imageOpData) driver.Texture {
-	type cachekey struct {
-		filter byte
-		handle any
-	}
-	key := cachekey{
+func (r *renderer) texHandle(cache *textureCache, data imageOpData) driver.Texture {
+	key := textureCacheKey{
 		filter: data.filter,
 		handle: data.handle,
 	}
@@ -1211,7 +1207,7 @@ func (d *drawState) materialFor(rect f32.Rectangle, off f32.Point, partTrans f32
 	return m
 }
 
-func (r *renderer) uploadImages(cache *resourceCache, ops []imageOp) {
+func (r *renderer) uploadImages(cache *textureCache, ops []imageOp) {
 	for i := range ops {
 		img := &ops[i]
 		m := img.material