I have following dropdown options
```
[
["no matter", ""]
["Update", "true"]
["Command", "false"]
]
```
In case my value is "" the text is not filled with "no matter" by the initial draw and the empty selector is shown. I expect the text "no matter"
This PR fixes that
Replace the fixed dropdown height with one responsive to the document's viewport.
This is adapted from Bohdan-Tereta's proposed solution:
https://github.com/google/blockly/pull/1483#issuecomment-381638639
It is sub-optimal, in that is does not adapt to field height (variable
due to workspace zoom), and it does not fully utilize the space above
or below the field if the block is near the top or the bottom.
Implement #1584 - Fields now registered by their JSON type name, allowing new custom fields and overriding of the standard fields. Replaces the manual switch statement for loading fields from JSON block definitions.
* New widget div functions, used in context menu code
* Make all widget div positioning functions use the same argument order
* Use new widget div functions for fields
* share code for measuring menu size
* Get rid of positionMenu
* Update copyright date
* Rebuild blockly_uncompressed because there's a new require in town
* Helper functions for rendering an image or text option.
* Break showEditor_ into smaller helper functions
* More decomposition, and function comments.
Moving all `math.js` definitions into a single JSON array, complete with i18n syntax for all messages, dropdowns, and tooltips.
Adding Blockly.Extensions.buildTooltipForDropdown(..) to facilitate the creation and error-checking of tooltips that update based on the value of a dropdown.
Now warn on raw string in JSON 'extensions'.
Adding support for string table lookups in dropdown field labels specified in JSON.
Adds Blockly.utils.replaceMessageReferences() method to handle string replacement without interpolation tokens. Effectively uses the same old code, now moved into tokenizeInterpolation_(), which takes a parseInterpolationTokens option.
Replaces the direct JavaScript references (not pure JSON, and thus not portable).
Demonstrating this behavior in the logic_boolean dropdown.
