[DomCrawler] added support for HTML5 'form' attribute
merged branch kepten/ticket_7486 (PR #7500)

This PR was merged into the master branch.

Discussion
----------

[DomCrawler] added support for HTML5 'form' attribute

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7486
| License       | MIT
| Doc PR        |

Commits
-------

f8178dd [DomCrawler] added support for HTML5 'form' attribute