Support dynamic properties on Blocks

[RoboErikG]

We should ensure we support dynamic components on blocks to match web.

• Dropdowns - Currently an array of key/value strings, needs update
• Tooltips - Currently a String, needs update

[RoboErikG]

@rachel-fenichel please check if there are any other dynamic components then unassign yourself.

[vicng]

Can someone link to code for where the dropdown one is implemented in web? I'm not aware of that one.

[RoboErikG]

https://github.com/google/blockly/blob/master/core/field_dropdown.js#L288

[rachel-fenichel]

See google/blockly-android#531