Permit single field disabling (#4932) (#4941)
Permit single field disabling (#4932) (#4941)

* Permit single field disabling (https://github.com/google/blockly/issues/4932)

* Permit single field disabling (#4932)

* Fixed lint error (moved && to end of line and adjusted line breaks accordingly)

* Added XML Field (De)Serialization

* Call parent method in FieldDropdown's fromXml
* Added protected helper methods to handle serialization/deserialization of enabled property/attribute of fields
* Minor changes to annotations to account for field disabling and 4 spaces per line break per style guide

* Revert "Added XML Field (De)Serialization"

This reverts commit 1964e866b6ab5c1615522f0a7a634a7ea9a9004b.

* Comment style changes

* Comment reversions

* Indentation fix

* Indentation reversion
google/blockly,rachel-fenichel/blockly,mark-friedman/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,rachel-fenichel/blockly,google/blockly,mark-friedman/blockly,google/blockly,rachel-fenichel/blockly,mark-friedman/blockly,google/blockly,mark-friedman/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,mark-friedman/blockly,mark-friedman/blockly