[core] Add helper functions for clamp_at_... (#10387)

tests/components/esp8266/test.esp8266-ard.yaml

@@ -0,0 +1,13 @@
+logger:
+  level: VERBOSE
+
+esphome:
+  on_boot:
+    - lambda: |-
+        int x = 100;
+        x = clamp(x, 50, 90);
+        assert(x == 90);
+        x = clamp_at_least(x, 95);
+        assert(x == 95);
+        x = clamp_at_most(x, 40);
+        assert(x == 40);