[Process] Add missing docblocks, remove variable declarations
minor #10756 [2.3][Process] Add missing docblocks, remove variable declarations (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
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[2.3][Process] Add missing docblocks, remove variable declarations

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT

Commits
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ff77f24 [Process] Add missing docblocks, remove variable declarations
Merge branch '2.3' into 2.4

* 2.3:
  [Process] Add missing docblocks, remove variable declarations

Conflicts:
	src/Symfony/Component/Process/ProcessBuilder.php