feat: allow setting window shape (backport: 3-0-x) (#14445)

* feat: allow setting window shape

This binds Widget::SetShape, an API that already exists in Chromium (for
Windows and Linux). It's a more reliable method of having some parts of
your window be "click-through" than the current `setIgnoreMouseEvents`
API, which messes around with the `WS_EX_LAYERED` window style on
Windows, causing strange bugs and incompatibility with hardware
acceleration.

* update docs

spec/api-browser-window-spec.js

@@ -893,6 +893,17 @@ describe('BrowserWindow module', () => {
     })
   })
 
+  describe('BrowserWindow.setShape(rects)', () => {
+    it('allows setting shape', () => {
+      assert.doesNotThrow(() => {
+        w.setShape([])
+        w.setShape([{x: 0, y: 0, width: 100, height: 100}])
+        w.setShape([{x: 0, y: 0, width: 100, height: 100}, {x: 0, y: 200, width: 1000, height: 100}])
+        w.setShape([])
+      })
+    })
+  })
+
   describe('"useContentSize" option', () => {
     it('make window created with content size when used', () => {
       w.destroy()