Migrate private static fields/functions in core/field_dropdown.js to module-internal
Migrate private static fields/functions in core/field_dropdown.js to module-internal

google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,mark-friedman/blockly,rachel-fenichel/blockly,google/blockly,mark-friedman/blockly,google/blockly,mark-friedman/blockly,rachel-fenichel/blockly,mark-friedman/blockly,mark-friedman/blockly,rachel-fenichel/blockly,mark-friedman/blockly,google/blockly,rachel-fenichel/blockly,google/blockly,google/blockly