feat: control Flow Editor via the Electron app menu

[yeze322]

Description

closes #3227

Problem

In Electron app, there are a group of menu items under the system menu -> 'Edit' label which are designed to share the same functionality with Composer Toolbar (Undo/Redo/Cut/Copy/Del).

However, they never work due to not connected to editor events.

Target

This PR connected Composer editor APIs with the Electron app menu bar to fix this issue.
Supported actions:

• 'undo' (api not provided by Shell, WIP by @lei9444 )
• 'redo' (api not provided by Shell, WIP by @lei9444 )
• 'copy'
• 'cut'
• 'delete'
• 'paste' (paste is available in the flyout action menu)

How it works

Electron app menu runs in main process; Composer web app runs in renderer process.
To connect them together, we can leverage Electron IPC mechanism to let 'main' process post messages to 'renderer' process.

// main process (app menu) -> post messages
rendererWindow.webContents.send('event-name', eventData);

// renderer process (Composer webapp) -> subscribe events
ipcRenderer.on('event-name', (e, eventData) => handle(eventData));

Task Item

Screenshots

[yeze322]

@cwhitten Chris do you think it's a good solution to share those Composer APIs via the global window variable?

[coveralls]

Coverage decreased (-0.2%) to 57.313% when pulling b5288b5 on visual/appmenu into ba18903 on main.

[cwhitten]

@yeze322 this seems reasonable. We wouldn't want to enable those actions if there was no current node selection, so we need to add a enabled/disabled heuristic. cc @tonyanziano

[yeze322]

Feature completed, ready for review and test.
I've tested on Windows platform.

[cwhitten]

See my earlier comment on needing to wire up a disabled/enabled heuristic. It needs to match what options are available in the authoring surface.

[yeze322]

See my earlier comment on needing to wire up a disabled/enabled heuristic. It needs to match what options are available in the authoring surface.

Updated the logic: Composer (renderer process) send an actionSelected status to Electron menu (main process) to control Electron's app menu status.

[yeze322]

@cwhitten I updated the code to fix UT.

Ideally, the failure on undefined ipcMain should be fixed by providing a mocked Electron package under __mock__/Electron.js, however, to make the fix simple, I just check the existence of ipcMain.