Pulls from MakeCode fork the ability to rename and delete variables i…

[alschmiedt]

…n flyout

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide

The details

Resolves

#1105

Proposed Changes

Adds ability to rename and delete a variable through the context menu in the variable flyout. Discussed here: #2143

.

Reason for Changes

So that users can delete or rename a variable without first having to drag it into the workspace.

Test Coverage

Tested on:

Additional Information

This code is pulled from the MakeCode fork found here: microsoft/pxt-blockly@2537e07

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[RoboErikG]

LGTM