[Form] deprecated "property_path" in favor of "map_to"

[Form] deprecated "property_path" in favor of "map_to"

 Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #7832
| License       | MIT
| Doc PR        | no
This method should be removed from the interface (not the implementation) if the new `setMapTo` method is introduced. But I'm not sure if @webmozart only meant to rename the __option__ and leave the method name as-is.