Type issues in dev-tools test helpers

[rachel-fenichel]

Component

dev-tools

Describe the bug

Some of the types are wrong or don't make sense.

In particular:

• In block_test_helpers.mocha.js, CodeGenerationTestCase is tagged with @implements {TestCase}, from common_test_helpers.mocha.js, but TestCase is a class, not an interface.
• Same issue with FieldValueTestCase
• FieldCreationTestCase is tagged with @extends {FieldValueTestCase}, but doesn't have extends in the class declaration (or a super() call in the constructor.
• populateRandom in populate_random.js has a parameter of type Blockly.Workspace but it should be a Blockly.WorkspaceSvg--we assume it is later, when calling initSvg() and similar functions on the return value of workspace.newBlock().
• screenshot.js is doing some things that I don't understand with Rect objects.

Additional information @NeilFraser found these issues while working on fields.

[maribethb]

We're not actually running the Closure compiler on these in samples. We should

• remove the Closure-style annotations that don't make sense
• update the code to actually use extends, etc. where appropriate
• consider converting to TS

Also, an editor might complain with red squiggly lines, but I don't think this is blocking actually running the tests.

[rachel-fenichel]

@gonfunko were you looking at this one?

[gonfunko]

I was, but it was pretty rapidly expanding in scope.

[rachel-fenichel]

Cool, so it's still in the queue