refactor(time): refactor delay with input checking

Previously, there were three low-level delay entry points

- os_delay(ms, ignoreinput=true): sleep for ms, only break on got_int

- os_delay(ms, ignoreinput=false): sleep for ms, break on any key input
  os_microdelay(us, false): equivalent, but in μs (not directly called)

- os_microdelay(us, true): sleep for μs, never break.

The implementation of the latter two both used uv_cond_timedwait()
This could have been for two reasons:
 1. allow another thread to "interrupt" the wait
 2. uv_cond_timedwait() has higher resolution than uv_sleep()

However we (1) never used the first, even when TUI was a thread, and
(2) nowhere in the codebase are we using μs resolution, it is always a ms
multiplied with 1000.

In addition, os_delay(ms, false) would completely block the thread for
100ms intervals and in between check for input. This is not how event handling
is done alound here.

Therefore:

Replace the implementation of os_delay(ms, false) to use
LOOP_PROCESS_EVENTS_UNTIL which does a proper epoll wait with a timeout,
instead of the 100ms timer panic.

Replace os_microdelay(us, false) with a direct wrapper of uv_sleep.

src/nvim/ui.c

@@ -439,7 +439,7 @@ void ui_line(ScreenGrid *grid, int row, int startcol, int endcol, int clearcol,
                              MIN(clearcol, (int)grid->cols - 1));
     ui_call_flush();
     uint64_t wd = (uint64_t)labs(p_wd);
-    os_microdelay(wd * 1000U, true);
+    os_sleep(wd);
     pending_cursor_update = true;  // restore the cursor later
   }
 }
@@ -521,7 +521,7 @@ void ui_flush(void)
   ui_call_flush();
 
   if (p_wd && (rdb_flags & RDB_FLUSH)) {
-    os_microdelay((uint64_t)labs(p_wd) * 1000U, true);
+    os_sleep((uint64_t)labs(p_wd));
   }
 }