gpui: Sweep through cargo doc output and mark dubious items as non-public (#3932)

I essentially went through the publicly exported items and marked these
that are e.g. leaky reexports as pub(crate). I expect that'd be done on
Tuesday anyways.

Release Notes:
- N/A

crates/gpui/src/platform/mac/dispatcher.rs

@@ -13,9 +13,14 @@ use parking::{Parker, Unparker};
 use parking_lot::Mutex;
 use std::{ffi::c_void, ptr::NonNull, sync::Arc, time::Duration};
 
-include!(concat!(env!("OUT_DIR"), "/dispatch_sys.rs"));
+/// All items in the generated file are marked as pub, so we're gonna wrap it in a separate mod to prevent
+/// these pub items from leaking into public API.
+pub(crate) mod dispatch_sys {
+    include!(concat!(env!("OUT_DIR"), "/dispatch_sys.rs"));
+}
 
-pub fn dispatch_get_main_queue() -> dispatch_queue_t {
+use dispatch_sys::*;
+pub(crate) fn dispatch_get_main_queue() -> dispatch_queue_t {
     unsafe { &_dispatch_main_q as *const _ as dispatch_queue_t }
 }