feat!: delete angle, colour, and multiline input fields and blocks

[rachel-fenichel]

The basics

• I validated my changes

The details

Resolves

Fixes #7226

Proposed Changes

• Delete angle field and associated mocha tests from core.
• Delete colour field and associated mocha tests from core.
• Delete colour blocks, associated generators, and associated generator tests from core.
• Delete multiline text field and associated mocha tests from core.
• Delete multiline text block, associated generators, and associated generator tests from core.

Reason for Changes

Delete fields that have been moved to plugins, along with their associated blocks and generators.

Test Coverage

For generators: I deleted the relevant test suite from the generator test page, then ran the generator tests and executed each language's code to verify that it still works (or has no new bugs, in the case of PHP). I then read through the diff to make sure the changes made sense and committed the new generated code as the new golden file.

Re-adding serializer tests is tracked in google/blockly-samples#2237

Documentation

Tracked in #7245

Additional Information

BREAKING CHANGE: This change deletes the colour field, angle field, and multiline text input field. All three are now provided as plugins. The blocks associated with the colour field and multiline text field have been moved to the field plugins, whic now provide documentation on how to install the blocks.