Rename Field Capabilities

[stevejgordon]

Per discussion in #5200 for 8.0.0 we should resolve a naming issue in FieldCapabilitiesResponse where we now have two concepts of "version". The original Version property should be renamed as DocVersion to distinguish it as a special field type. The VersionField added in 7.11.0 can then be renamed to Version.

This is a breaking change, hence it needs to be completed in master for 8.0.0 only.

[stevejgordon]

Code-gen