zink: disable fbfetch when flushing clears

this ensures there's no weird perf happening, avoids using renderpass
instead of dynamic rendering, and avoids hitting an assert from broken
framebuffer construction

cc: mesa-stable

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19065>
(cherry picked from commit d3880a6324)

.pick_status.json

@@ -715,7 +715,7 @@
         "description": "zink: disable fbfetch when flushing clears",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/gallium/drivers/zink/zink_context.c

@@ -3400,9 +3400,18 @@ zink_flush(struct pipe_context *pctx,
    unsigned submit_count = 0;
 
    /* triggering clears will force has_work */
-   if (!deferred && ctx->clears_enabled)
+   if (!deferred && ctx->clears_enabled) {
+      /* if fbfetch outputs are active, disable them when flushing clears */
+      unsigned fbfetch_outputs = ctx->fbfetch_outputs;
+      if (fbfetch_outputs) {
+         ctx->fbfetch_outputs = 0;
+         ctx->rp_changed = true;
+      }
       /* start rp to do all the clears */
       zink_batch_rp(ctx);
+      ctx->fbfetch_outputs = fbfetch_outputs;
+      ctx->rp_changed |= fbfetch_outputs > 0;
+   }
 
    if (ctx->needs_present && (flags & PIPE_FLUSH_END_OF_FRAME)) {
       if (ctx->needs_present->obj->image)