test: Add support for Typescript tests in core

[gonfunko]

The basics

• I validated my changes

The details

Proposed Changes

This PR adds support for writing tests for core Blockly in Typescript, and converts some of the existing tests that are trivially convertible. It also resolves a few bugs related to calling new on non-constructors in the JS tests that TSC surfaced.

Once this is merged, we can and should begin gradually converting the remainder of the test suite to Typescript, and use Typescript for all newly-introduced test files. A few notes regarding best practices:

• Typescript tests should not stick things onto this to share state between setup and tests. Instead, they should declare variables at the top-level suite, assign them in setup, and reference them in tests. This ensures that everything typechecks; lint will yell at you if you try to tack things on to this.
• Relatedly, TS tests must pass the workspace under test to sharedTestTeardown()
• TS tests must always import * as Blockly from '#core/blockly.js'; as well as importing sinon and chai where needed. If a TS test exercises something that is not exported from core, they may import it by path relative to #core. In general, this pattern should address Use Blockly consistently in mocha tests #7224 once the entire suite is converted – always import and use Blockly, unless testing something that isn't exported, in which case import it directly.

Reason for Changes

Better typechecking catches bugs and forces us to be less sloppy in our tests.