fix: Update Blockly dependencies and api calls

[moniika]

This PR:

• Updates the peerDependency and devDependency of plugins so that they can be tested with Blockly beta
• Updates Blockly.Marker to Blockly.Marker.Marker in the keyboard_nav plugin (changed in Blockly beta release)

[moniika]

Filed issue #902 to investigate error encountered when running tests with Blockly core beta installed.

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[alschmiedt]

Closes this as it is leftover from the last release.