changed the ESI fragment renderer to be always registered
merged branch fabpot/esi-fragment-handler (PR #8730)

This PR was merged into the master branch.

Discussion
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changed the ESI fragment renderer to be always registered

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

This is an alternative implementation for #8427

Commits
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09f727b changed the ESI fragment renderer to be always registered