Use HIGH priority to wake blocked timers (#11269)

One contributor to some beach-balls was that the main thread was calling
block_with_timeout, but the timeout never fired.

Release Notes:

- Reduced main thread hangs under very high system load

crates/gpui/build.rs

@@ -47,7 +47,6 @@ mod macos {
             .header("src/platform/mac/dispatch.h")
             .allowlist_var("_dispatch_main_q")
             .allowlist_var("_dispatch_source_type_data_add")
-            .allowlist_var("DISPATCH_QUEUE_PRIORITY_DEFAULT")
             .allowlist_var("DISPATCH_QUEUE_PRIORITY_HIGH")
             .allowlist_var("DISPATCH_TIME_NOW")
             .allowlist_function("dispatch_get_global_queue")