add keyboard.disableRotation and tests

[jmbott]

fix #3768

adds the option to disable and enable map rotation from the keyboard,

// disable
map.keyboard.disableRotation();
// enable
map.keyboard.enableRotation();

similar to,

// disable
map.touchZoomRotate.disableRotation();
// enable
map.touchZoomRotate.enableRotation();

so you do not have to disable all zooming and panning options the keyboard can provide with map.keyboard.disable().

adds unit tests to support,

• map still pans when rotation disabled
• map does not rotate when rotation is disabled
• map does not tilt when rotation is disabled
• map still zooms when rotation is disabled

Launch Checklist

• briefly describe the changes in this PR
• include before/after visuals or gifs if this PR includes visual changes
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
• tagged @mapbox/map-design-team @mapbox/static-apis if this PR includes style spec API or visual changes
• tagged @mapbox/gl-native if this PR includes shader changes or needs a native port
• apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'
• add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog>adds disableRotation() and enableRotation() to KeyboardHandler</changelog>

@mapbox/map-design-team @mapbox/static-apis adds to KeyboardHandler instance members

• https://docs.mapbox.com/mapbox-gl-js/api/map/#map#keyboard
• https://docs.mapbox.com/mapbox-gl-js/api/handlers/#keyboardhandler

[mourner]

Thanks so much for the PR and extensive tests! Would you mind also adding JSDoc comments for the methods like in touch_zoom_rotate.js for completeness while we're at it? Should be mostly copy-paste.

[jmbott]

@mourner Thank you for the review! Added JSDoc comments for keyboard.js. Let me know if anything else is required.