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.
#11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle
feature #11869 #11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle (hacfi)

This PR was squashed before being merged into the 2.6-dev branch (closes #11869).

Discussion
----------

#11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes, deprecation targets 3.0
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #11652
| License       | MIT
| Doc PR        | - (Not mentioned in the docs)

Commits
-------

86873f2 #11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle
#11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle
feature #11869 #11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle (hacfi)

This PR was squashed before being merged into the 2.6-dev branch (closes #11869).

Discussion
----------

#11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes, deprecation targets 3.0
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #11652
| License       | MIT
| Doc PR        | - (Not mentioned in the docs)

Commits
-------

a777fd7 #11652 [HttpKernel] Remove unused method Kernel::isClassInActiveBundle
feature #11549 [Bundle][FrameworkBundle] make the stopwatch service always available (xabbuh)

This PR was merged into the 2.6-dev branch.

Discussion
----------

[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
-------

ffc4090 make the stopwatch service always available
[Debug] Symfony debug extension
[Debug] a README for the debug extension
[VarDumper] algo to clone any PHP variable to a breadth-first queue
[VarDumper] symfony_debug ext. fast and memory efficient cloning algo
[VarDumper] add casters for per class/resource custom state extraction
[VarDumper] casters for exceptions representation
[VarDumper] casters for SPL data structures
[VarDumper] casters for PDO related objects
[VarDumper] casters for Doctrine objects
[VarDumper] casters for DOM objects
[VarDumper] interface for dumping collected variables
[VarDumper] CLI dedicated dumper and related abstract
[VarDumper] HTML variant of the CLI dumper
[VarDumper] spec for json based representation of PHP vars