Use consistent MinValue and MaxValue property names

The standard library uses inconsistent shared property names for minimum and maximum values across bounded scalar types. Currency already exposes MinValue and MaxValue, while Integer and Double expose Min and Max, and DateTime has MinValue but no maximum equivalent.

This proposal standardises bounded scalar types on MinValue and MaxValue as the canonical shared-property names:

• Add Integer.MinValue and Integer.MaxValue.
• Add Double.MinValue and Double.MaxValue (the most negative and largest positive finite Double values; Double.Infinity remains a separate value).
• Add the currently missing DateTime.MaxValue.
• Keep the existing Currency.MinValue and Currency.MaxValue.
• Retain Integer.Min, Integer.Max, Double.Min, and Double.Max as source-compatible, deprecated compatibility aliases.
• Do not add Currency.Min/Currency.Max or DateTime.Min/DateTime.Max.
• DateTime.Empty remains unchanged and is still the preferred representation for an unset date.

The migration is additive and source compatible: existing code using the short names continues to compile and run, with a normal deprecation warning.