fix: Change how dev-tools adds Blockly to the global scope for console debugging

[rachel-fenichel]

Previously this reached into Blockly.utils.global to make sure that it was getting the same global object as the rest of Blockly.

After this change the code uses globalThis. It won't work in IE, but much of dev-tools and our mocha/sinon test setup does not work in IE.

We add Blockly to the global object to simplify manual debugging from the console while using dev-tools. It's not necessary for automated tests.

Tested by building and starting the dev-tools package locally and inspecting the value of Blockly in the console. Also tested by removing the line entirely to make sure that Blockly was not being added to the global scope somewhere else.

[cpcallen]

Also tested by removing the line entirely to make sure that Blockly was not being added to the global scope somewhere else.

For posterity: core/msg.js in Blockly does add a Blockly entry to the global namespace, containing only Blockly.Msg.