chore(deps): Update blockly dev dependency to blockly@12.0.0-beta.4

[cpcallen]

The basics

• I validated my changes

The details

Proposed Changes

• Fix clean:node npm script that was inadvertently broken by a mistranscription in PR fix: add lerna commands to plugins package.json #2453.
• Bump blockly dev dependency to v12.0.0-beta.4.
• Fix type of FieldColour.prototype.isFullBlockField, as superclass method becomes public in v12.0.0.
• Fix FieldMultilineInput to not depend on Field.NBSP, which was temporarily removed.
  • Include a TODO to reinstate use of .NBSP where appropriate.
• Fix FieldGridDropdown to not fail type checking due to the introduction of spacers.

Reason for Changes

Keep samples working with v12.

Test Coverage

Passes npm test (at least, I think it does—FieldDate tests always fail when tested outside the US!)

Have not done manual testing of individual plugins.

[cpcallen]

@RoboErikG or anyone on the team: I recommend you merge this once it has been approved. Can't auto-merge due to there being no rule blocking merge without review.

[BenHenning]

Thanks @cpcallen. Going ahead and approving to unblock.

[BenHenning]

Though, I think there are other failures still @cpcallen.

Dismissing since CI is failing.

[cpcallen]

OK, despite what GitHub is currently telling me ("All checks have passed"), the keyboard-navigation plugin is still unbuildable due to too many breaking changes in core. I was going to delete it in this PR but remembered that that might cause many other plugins to get a major version bump, so I separated the deletion out into #2508.

This PR's tests should all pass once that PR has been merged.

N.B. there have been additional commits added since @BenHenning approved.

[cpcallen]

Superceded by #2509.

[cpcallen]

OK, #2509 had test failures in CI that I did not discover when running test locally, so I'm going to reopen this one for now and leave the update to -beta.5 until I can fix those test failures.

[maribethb]

Going to merge this so can do the .5 changes separately.