feat(Typescript): Use internal, OpenAPI-generated, types for Compute, GCS, Groups, and Timer.

[jbottigliero]

• All services that have OpenAPI specs now export a type OpenAPI from their entrypoints.
• Adds script for generating types from the OpenAPI resources.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.72%. Comparing base (a63c137) to head (72127ee).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #447   +/-   ##
=======================================
  Coverage   98.72%   98.72%           
=======================================
  Files          72       72           
  Lines        1254     1254           
  Branches      210      210           
=======================================
  Hits         1238     1238           
  Misses         15       15           
  Partials        1        1           

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