[Form] Added form debug collector
[Form] Merged subsriber/collector, also collect valid forms
[Form] Decoupled methods of ResolvedFormType so that they can be overridden individually by decorators
[HttpKernel] Extracted value exporting logic of DataCollector into a separate ValueExporter class
[Form] Improved form debugger
merged branch bschussek/form-debugger (PR #9082)

This PR was merged into the master branch.

Discussion
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[Form] Implemented form debugger

Same as #9021 (kudos to @digitalkaoz!), with some added caramel.

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

**Note:** Please keep in mind that this is a first version only. Not all features (especially UX/UI-wise) that I'd like to see are in there, but it's good enough for a first merge.

Commits
-------

89509d9 [Form] Improved form debugger
f56c577 [HttpKernel] Extracted value exporting logic of DataCollector into a separate ValueExporter class
56d78ed [Form] Decoupled methods of ResolvedFormType so that they can be overridden individually by decorators
a994a5d [Form] Merged subsriber/collector, also collect valid forms
1972a91 [Form] Added form debug collector