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/Condition.zig

@@ -115,7 +115,7 @@ pub const AtomicCondition = struct {
                             else => unreachable,
                         }
                     },
-                    else => spinLoopHint(),
+                    else => std.atomic.spinLoopHint(),
                 }
             }
         }