[DomCrawler] Fixed charset detection in html5 meta charset tag
bug #10983 [DomCrawler] Fixed charset detection in html5 meta charset tag (77web)

This PR was squashed before being merged into the 2.3 branch (closes #10983).

Discussion
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[DomCrawler] Fixed charset detection in html5 meta charset tag

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

It may be minor to folks with ascii-charactered language, but is critical for us Japanese.
Many Japanese websites with SJIS encoding have "Shift_JIS" as their encoding declaration.

Commits
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172e752 [DomCrawler] Fixed charset detection in html5 meta charset tag