[Twig][Form] Moved configuration key twig.form.resources to twig.form_themes
feature #11343 [Twig][Form] Moved twig.form.resources to a higher level (stefanosala)

This PR was merged into the 2.6-dev branch.

Discussion
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[Twig][Form] Moved twig.form.resources to a higher level

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #11296
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/4003

Commits
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ab0b5e6 [Twig][Form] Moved configuration key twig.form.resources to twig.form_themes