Expose Screen Reader Mode over the iframe API

[microbit-matt-hillsdon]

Adds a "togglescreenreadermode" editor message that behaves like the settings menu toggle (including the "settings" telemetry event source), and reports the current state via a new screenReaderMode field on the "info" response.

As part of this change I realised that toggleScreenReaderMode was async in implementation but not interface so I've aligned both to be async.

Needed for micro:bit classroom to expose the same setting.

I'm hopeful that this is our last change!

[microbit-matt-hillsdon]

@riknoll would be great to get this one in if possible.

[Copilot]

Pull request overview

Exposes the editor’s Screen Reader Mode toggle via the iframe message API and reports the current state in the info response, aligning the project view API to reflect that the underlying implementation is async.

Changes:

• Route the Settings menu and Blockly shortcut toggles through toggleScreenReaderModeAsync(...) in ProjectView.
• Add togglescreenreadermode as an editor message and include screenReaderMode in the info response.
• Update IProjectView typings to include toggleScreenReaderModeAsync(...) and isScreenReaderModeEnabled().

Show a summary per file

File	Description
webapp/src/container.tsx	Update Settings menu screen reader toggle to call the async project view method.
webapp/src/blocks.tsx	Update Blockly screen reader shortcut handler to call the async project view method.
webapp/src/app.tsx	Rename/adjust project view screen reader toggle to async method and add state getter.
pxteditor/editorcontroller.ts	Add new togglescreenreadermode message handling and report state via info.
localtypings/pxteditor.d.ts	Extend iframe message/action and project view typings to include the new API surface.

Review details

• Files reviewed: 4/5 changed files
• Comments generated: 3
• Review effort level: Low

[microbit-matt-hillsdon]

Thanks @riknoll. No worries if this doesn't make the release so long as it can be ported across soon.