Generate and commit TypeScript declaration files

[hparra]

Improve devex for TS users.

Types of changes

• 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 change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[hparra]

Build failures don't seem to be related to changes. main ok?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e09f888) to head (def5270).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #57   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines          132       132           
  Branches        24        24           
=========================================
  Hits           132       132           

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[shazron]

test failure here: wait for #60 to be reviewed and pulled in, then merge