Calling getField/getFieldValue/setFieldValue without supplying name gets/changes (value of) first unnamed field

[jschanker]

Calling block.setFieldValue without supplying the field name for the required second parameter results in the block's first unnamed field being set to the value of the first argument. For example, calling it on a built-in text_print block replaces print with whatever the new value that's passed is. Connected to this, calling block.getField or block.getFieldValue without supplying a name of the field (value) to get returns the block's first unnamed field (value).

To Reproduce

Steps to reproduce the behavior:

1. Go to https://blockly-demo.appspot.com/static/tests/playground.html
2. Drag in a text_print block.
3. Open the Developer console and type Blockly.getMainWorkspace().getAllBlocks()[0].setFieldValue("Blockly")
4. See the text print change to Blockly.

Expected behavior

Throw an error when calling setFieldValue without specifying the name of the field to set and throw a warning or error when calling getField or getFieldValue without specifying the name of the field (of the value) to get.

[cpcallen]

Fixed by PR #4876 4876