- part II of II for #2445
- `FormCollectionModelBinder` is an exception because container is not user-provided
- no `ModelState` entry added
- enable tests that #2445 was blocking
- fix these and other tests expecting different `ModelState` entries
- simplify logic in `FormFileModelBinder`
`ValueProviderResult`
- remove `protected` setters and parameterless constructor
- no scenario for their use in subclasses; however `ConvertTo()` remains `virtual`
- add single-parameter constructor
- use in most of the greedy and type-matching model binders
- add doc comments throughout class
nits:
- use new `ValueProviderResult` constructor in many existing tests
- `""` -> `string.Empty` and `vpr` -> `valueProviderResult` in `ValueProviderResultTest`
- improve some test names in `BodyValidationIntegrationTests`
- do not check `Message` of a Json.NET `Exception`
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