make the stopwatch service always available

Previously, one had to be careful to check if the debug.stopwatch
service was available before using it. Otherwise, the application
would break in the prod environment.
feature #11549 [Bundle][FrameworkBundle] make the stopwatch service always available (xabbuh)

This PR was merged into the 2.6-dev branch.

Discussion
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[Bundle][FrameworkBundle] make the stopwatch service always available

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11347
| License       | MIT
| Doc PR        |

Previously, one had to be careful to check if the ``debug.stopwatch`` service was available before using it. Otherwise, the application would break in the prod environment.

Commits
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ffc4090 make the stopwatch service always available