support for is-gesture (#1873)

* support for is-gesture

* updated shims

* activate shake button

* refactor

* refactor shake button

docs/reference/input/is-gesture.md

@@ -0,0 +1,28 @@
+# Is Gesture
+
+Tests if a gesture is currently detected.
+
+```sig
+input.isGesture(Gesture.Shake)
+```
+
+## Parameters
+
+* ``gesture`` means the way you hold or move the @boardname@. This can be `shake`, `logo up`, `logo down`, `screen up`, `screen down`, `tilt left`, `tilt right`, `free fall`, `3g`, or `6g`.
+
+## Example: random number
+
+This program shows a number from `2` to `9` when you shake the @boardname@.
+
+```blocks
+forever(function() {
+    if (input.isGesture(Gesture.Shake)) {
+        let x = Math.randomRange(2, 9)
+        basic.showNumber(x)
+    }
+})
+```
+
+## See Also
+
+[on gesture](/reference/input/on-gesture)