[Form] Fix of "PATCH'ed forms are never valid"

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8111
| License       | MIT
Added missing files .gitignore
merged branch biozshock/patch-form-fix (PR #8362)

This PR was merged into the 2.3 branch.

Discussion
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[Form] Fix of "PATCH'ed forms are never valid". Fixes #8111

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8111
| License       | MIT

Commits
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a2b1535 [Form] Fix of "PATCH'ed forms are never valid"
Merge branch '2.3'

* 2.3:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary
  Added missing files .gitignore
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class
  [Form] Fix of "PATCH'ed forms are never valid"