use meta charset in layouts without legacy http-equiv
minor #12192 use meta charset in layouts without legacy http-equiv (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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use meta charset in layouts without legacy http-equiv

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

`<meta charset="UTF-8" />` is now the recommended approach

Commits
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96e7b01 use meta charset in layouts without legacy http-equiv