std.sync.atomic: extended atomic helper functions (#8866)

- deprecates `std.Thread.spinLoopHint` and moves it to `std.atomic.spinLoopHint`
- added an Atomic(T) generic wrapper type which replaces atomic.Bool and atomic.Int
- in Atomic(T), selectively expose member functions depending on T and include bitwise atomic methods when T is an Integer
- added fence() and compilerFence() to std.atomic

lib/std/Thread/StaticResetEvent.zig

@@ -182,7 +182,7 @@ pub const AtomicEvent = struct {
                 timer = time.Timer.start() catch return error.TimedOut;
 
             while (@atomicLoad(u32, waiters, .Acquire) != WAKE) {
-                std.os.sched_yield() catch std.Thread.spinLoopHint();
+                std.os.sched_yield() catch std.atomic.spinLoopHint();
                 if (timeout) |timeout_ns| {
                     if (timer.read() >= timeout_ns)
                         return error.TimedOut;
@@ -293,7 +293,7 @@ pub const AtomicEvent = struct {
                         return @intToPtr(?windows.HANDLE, handle);
                     },
                     LOADING => {
-                        std.os.sched_yield() catch std.Thread.spinLoopHint();
+                        std.os.sched_yield() catch std.atomic.spinLoopHint();
                         handle = @atomicLoad(usize, &event_handle, .Monotonic);
                     },
                     else => {