feat: allow the dialog methods to take in extra parameters

[BeksOmega]

The basics

• I validated my changes

The details

Resolves

Fixes #7882

Proposed Changes

Makes it so the setX dialog methods assign directly to the property on the exported namespace tree instead of to an internal variable.

Reason for Changes

Fixes a problem for Scratch where they didn't have a good place for their dialog code to live.

Test Coverage

Added tests that assigned dialogmethods can take in extra parameters.

Documentation

This is pretty niche so I don't think it needs explicit documentation.

Additional Information

This doesn't have to go into v11, I just put it up against that in case it can be reviewed in time.

[cpcallen]

This PR is causing tests in blockly-samples repository to fail for typed-variable-modal—but seemingly only when I merge the master branch into rc/v11.0.0 (see google/blockly-samples#2348) and then link that against a locally-built version of Blockly from this repo's rc/v11.0.0 branch:

Error: Not implemented: window.alert
    at module.exports (webpack-internal:///./node_modules/jsdom/lib/jsdom/browser/not-implemented.js:9:17)
    at Window.eval [as alert] (webpack-internal:///./node_modules/jsdom/lib/jsdom/browser/Window.js:864:7)
    at Object.alert$$module$build$src$core$dialog (webpack-internal:///../../../blockly/dist/blockly_compressed.js:575:605)
    at TypedVariableModal.onConfirm_ (webpack-internal:///./src/TypedVariableModal.js:205:56)

Linking to the commit before this PR landed prevents the test failures.
Running tests directly in the blockly-samples repository's rc/v11.0.0 branch also does not exhibit test failures.

[cpcallen]

After discussing with @BeksOmega, our working theory was that the test failure was being caused by the call to sinon.stub() in the typed-variable-modal tests failing to successfully stub Blockly.dialog.alert now that that is export let alert = … rather than the previous export function alert(…).

Having looked at blockly_compressed.js, I can confirm that this does appear to be probable. Here is an extract from the compiled output for core/dialog.ts, rewriting for legibility:

var alert$$internal = (a,b) => {
  window.alert(a);
  b&&b()
},

module$build$src$core$dialog = {
  get alert(){ return alert$$internal },
  // ...
};

…where the object declared as module$build$src$core$dialog becomes Blockly.dialog.

In other words: Closure Compiler does correctly support export let, and does so by creating a get accessor method for the exported name. It will actually do this for export functions too, since function declarations are equivalent to var and thus also mutable—though it's clever enough to only emit get accessors for dynamic exports that are actually subject to subsequent assignment

It's possible in principle for such an accessor to be stubbed, but Sinon would have to use Object.defineProperty rather than a simple assignment, and it probably doesn't.