Refactor shared

[moniika]

The basics

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

The details

Resolves

Part of #4065

Proposed Changes

• Refactored logic for stubbing Blockly.utils.genUid into shared_helpers.js and updated usages.
• Refactored helper method for asserting Event values into shared_helpers (assertEventEquals)
• Created helper methods for assertions on spys for event firing
• Refactored comment_test.js event_test.js and trashcan_test.js to use new event test helpers
• Added test for testing emitting UI event for "trashcanOpen"

Reason for Changes

Test Coverage

Ran mocha tests.

Tested on:

• Desktop Chrome

Documentation

Additional Information

Test methods were refactored as helpers were developed to better fit the needs of multiple tests, causing multiple files to be touched.

#4062 fixes eslint errors on the PR.

Initially after this refactor the test failed when they were running concurrently, revealing that some tests cause events to be fired on a timeout which causes failures in other event tests. A bug was filed #4064 to further investigate and resolve this issue. As a temporary fix, the event queue is cleared when a stub is created for Blockly.Events.fire but it is not the ideal fix.

[moniika]

This fix seems to work.

However, I thought I had tested with this change at some point and it didn't work, but it works now.
I'm a little worried that this fixes most failures, but there's still "sometimes" failures, which is why I want to address this better in a follow up as part of #4064.

[moniika]

Upon investigation, there are other instances where Blockly.Events.fire is stubbed/spied such as in block_test.js and toolbox_test.js. I plan to address in a follow up PR, to reduce the amount of changes in this PR, but I expect the changes to be very similar to what I've done here.
These other tests I've found that are not stubbing them to fire immediately may also be part of the issue in #4064.