[GPU] Avoid stale texture state after invalidation

Check shared memory validity before marking textures up to date and installing watches. If the backing range was invalidated, leave the texture outdated so it can be reloaded later.

src/xenia/gpu/shared_memory.h

@@ -72,6 +72,10 @@ class SharedMemory {
   // ensures the host GPU memory backing the range are resident. Returns true if
   // the range has been fully updated and is usable.
   bool RequestRange(uint32_t start, uint32_t length);
+  // Returns whether every page in the range is currently valid in the host GPU
+  // memory copy. Hold the global critical region if relying on this for state
+  // transitions such as watch installation.
+  bool IsRangeValid(uint32_t start, uint32_t length) const;
 
   void TryFindUploadRange(const uint32_t& block_first,
                           const uint32_t& block_last,