Implement participant indicator for sessions

[izruff]

Description

Adds cursor display for other users in the same session and fixed related bugs.
This PR is associated with source-academy/sharedb-ace-backend#26 and source-academy/sharedb-ace#26

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Code quality improvements

How to test

Multiple users join the same session. Upon entering, cursors of other users should automatically show. Each cursor whenever updated will move to its new position and show a label containing the name of the user associated with it ("undefined" if no name is detected).

To test the sharedb-ace package locally, run yarn build then yarn link on the sharedb-ace repository, then run yarn link @sourceacademy/sharedb-ace on the frontend repository.

Checklist

• I have tested this code
• I have updated the documentation

[coveralls]

Pull Request Test Coverage Report for Build 9101316786

Details

• 3 of 6 (50.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.007%) to 31.417%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/commons/editor/UseShareAce.tsx	3	6	50.0%

Files with Coverage Reduction	New Missed Lines	%
src/commons/editor/UseShareAce.tsx	1	22.64%

Totals
Change from base Build 9101202777:	0.007%
Covered Lines:	4894
Relevant Lines:	14676

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💛 - Coveralls