update contrib autoloading and gitsplit

[brettmc]

• match grpc's gitsplit destination repo to match package name: 'transport-grpc'
• set autoload->files for contrib modules which support factory registry

[brettmc]

note to self: add transport-grpc to packagist after merge

• done

[codecov]

Codecov Report

Merging #875 (bcb22b9) into main (1ffd7e8) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #875   +/-   ##
=========================================
  Coverage     81.24%   81.24%           
  Complexity     2006     2006           
=========================================
  Files           264      264           
  Lines          5208     5208           
=========================================
  Hits           4231     4231           
  Misses          977      977           

Flag	Coverage Δ
7.4	80.72% <ø> (ø)
8.0	81.22% <ø> (ø)
8.1	81.36% <ø> (ø)

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