Form debugger storage
feature #9967 Form debugger storage (WouterJ)

This PR was squashed before being merged into the 2.5-dev branch (closes #9967).

Discussion
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Form debugger storage

This PR continues #9857

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9123
| License       | MIT
| Doc PR        | -

Commits
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744da7f Form debugger storage