Delete fields that were moved to samples out of core

[BeksOmega]

Check for duplicates

• I have searched for similar issues before opening a new one.

Problem

To actually make Blockly smaller when compressed, we need to delete the fields that were moved into samples out of core.

Request

Delete the fields from core.

Alternatives considered

N/A

Additional context

Dependent on #7225

Issues that tracked moving the fields:
google/blockly-samples#1646
google/blockly-samples#1645
google/blockly-samples#1644

[maribethb]

We put this in the Q3 project, but we haven't decided if we're doing a major release yet or not this quarter. So a PR for this should not be submitted until we've confirmed we plan to do a major release as this is a breaking change.

[maribethb]

Note google/blockly-samples#1733 needs to be fixed before this can be submitted as well.

[rachel-fenichel]

Issues to track additional work for moving block definitions into the field plugins:

• Field colour: add block definitions blockly-samples#2152
• Field angle: add block definitions blockly-samples#2153
• Multiline text field: add block definitions blockly-samples#2154
• Verify code demo will not be impacted by moving blocks to plugins #7826

[rachel-fenichel]

We also need to validate that all of the register functions (registerMutator, registerMixin, etc) can handle registering the same extension multiple times. The desired behaviour is:

• Check for any other functions that need to have the same behaviour
• Check the currently registered function and ensure it matches the one attempting to be registered. If so, silently accept the registration call and do nothing. If they don’t match, emit a warning or error.
• Update if needed

Rationale: An accepted pattern of use for fields is to unregister a field class, then register a substitute class under the same name. This allows users to install a default Blockly block but change the underlying field to one with different functionality.

Documentation: We may need to instruct users to unregister fields only after installing any blocks, so their objects are not overwritten by the built-in objects.