[Validator] Simplified usage of the Callback constraint
form_debug.xml should be loaded only if form config is enabled
merged branch tyx/fix/form-profiling (PR #9137)

This PR was merged into the master branch.

Discussion
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[Form] form_debug.xml should be loaded only if form config is enabled

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

Explication here:
https://github.com/symfony/symfony/commit/1972a916539d0bb877df9b16d373c272edd20cfd#commitcomment-4187567

Commits
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b668e24 form_debug.xml should be loaded only if form config is enabled
merged branch bschussek/issue2480 (PR #9133)

This PR was merged into the master branch.

Discussion
----------

[Validator] Simplified usage of the Callback constraint

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | fixes #2480, replaces #3939
| License       | MIT
| Doc PR        | symfony/symfony-docs#3012

Commits
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cccb1db [Validator] Simplified usage of the Callback constraint