refactor(ts): generate logging types from proto

[ofrobots]

Alternative to hand-writing the type-definitions #309.

[ofrobots]

The second step would be to check-in the generated proto/ directory. The proto typedefs will need to be updated very rarely, so it is not necessary to generate them on each CI.

[codecov]

Codecov Report

Merging #314 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #314   +/-   ##
=======================================
  Coverage   92.23%   92.23%           
=======================================
  Files          14       14           
  Lines         644      644           
  Branches       57       57           
=======================================
  Hits          594      594           
  Misses         36       36           
  Partials       14       14

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[ofrobots]

While we are here, we should also address https://github.com/googleapis/nodejs-logging/issues/133.

[ofrobots]

Re: #133, I believe the dynamic loadProto in

nodejs-logging/src/v2/logging_service_v2_client.js

Line 94 in 42262bf

gaxGrpc.loadProto(

can be replaced with a load of the statically generated proto/logging.js above. /cc @alexander-fenster