[Process] Fix docblocks, remove `return` from `PhpProcess#start()` as parent returns nothing, cleaned up `ExecutableFinder`
merged branch stloyd/bugfix/process_phpdocs (PR #6626)

This PR was merged into the 2.1 branch.

Commits
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a62e04f [Process] Fix docblocks, remove `return` from `PhpProcess#start()` as parent returns nothing, cleaned up `ExecutableFinder`

Discussion
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[2.1][Process] Fix docblocks, remove `return` from `PhpProcess#start()`
fixed CS