fix: fix bug that resulted in a variable dialog appearing atop the procedure editor dialog on mobile

[gonfunko]

This PR fixes gonfunko/scratch-blocks#169. Scratch doesn't use modal inputs on mobile like Blockly core does, but because this functionality wasn't being suppressed with the appropriate injection option, when the procedure editor modal was displayed, the default block, which has an editable text field, became focused, and on mobile caused a call to prompt(), resulting in the secondary dialog.

[rachel-fenichel]

Added google/blockly#8580 to document this option, since I was surprised to find it has no documentation.

I don't actually understand hwo this fixes the underlying problem. Why does the variable modal pop up from the procedure block?

[gonfunko]

When the Make a Block button is clicked to open the procedure editor, the starting block has the "block name" field which automatically gets focus. Without this change, on mobile, Blockly displays a modal dialog using `prompt()` to allow you to change the value of that field. Note that it isn't actually a variable dialog; Scratch swaps out the prompt implementation for one that looks at various passed-in fields, and depending upon the title configures the prompt for adding variables, lists, etc. The logic is such that it defaults to the "New Variable" title and the for this sprite/for all sprites option, but this is just a plain old prompt to modally edit a field value - note the "Change value" label for the text field, which is the only bit that actually does get passed into the prompt call.

[rachel-fenichel]

Note that it isn't actually a variable dialog; Scratch swaps out the prompt implementation

Got it, this was the piece I was missing.