Move AbLegacyDriverOptions, AbLegacyDataType enum, and
AbLegacyPlcFamilyProfile (including AbLegacyPlcFamily enum) to a new
Driver.AbLegacy.Contracts sibling project. All three files are zero-dep
after splitting AbLegacyDataTypeExtensions (which uses DriverDataType
from Core.Abstractions) into a new file that stays in the runtime driver.
Drop the doc-comment <see cref="AbLegacyAddress.TryParse"/> reference and
replace with <c>AbLegacyAddress.TryParse</c> per the approved decision.
The PlcFamilies using directive is retained in the contracts project since
both namespaces live there.
The runtime Driver.AbLegacy project gains a ProjectReference to .Contracts;
the .slnx is updated accordingly.
Joseph Doherty