Add manageEphemeralFocus parameter to dropdown show functions

[microbit-robert]

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Description

For field editors where MakeCode uses both the widget div and the dropdown div in combination, this ephemeral focus error is raised. Unlike the Blockly samples field slider plugin, in MakeCode, focus is moved to the HTML input, not the dropdown, so the ephemeral focus handling needs to be on the widget, not the dropdown div.

Please can you add an extra parameter for manageEphemeralFocus to showPositionedByField and showPositionedByBlock, which can then be passed to showPositionedByRect. At the moment, manageEphemeralFocus defaults to true and no callers pass this arg in core.

Reproduction steps

Stack trace

Screenshots

Example of the type of block affected, note the focus on the HTML input on opening:

Browsers

No response

[BenHenning]

For triage: I suspect that this is a P1 given that it's blocking some MakeCode scenarios and would require monkeypatching to work around without a proper fix in core Blockly.

[microbit-matt-hillsdon]

I hadn't initially realised, but this has broken blocks with these fields for mouse users in MakeCode too so likely blocks our upgrade to >= 12.0.0.

There are weird consequences beyond the field editor not working, e.g. clicking such an input field seems to get a block stuck in drag mode. Try e.g. "set volume" block in Music on this deployment built from Blockly develop.