Most of the AsXyz properties in BsonValue are simple casts that don't do any real conversion between types. But the AsDateTime and related properties actually do a type conversion because BsonDateTime and DateTime have different ranges and resolutions, as well the question of whether to convert to local or universal time.

The following changes will be made:

Deprecate AsDateTime: use ToLocalTime or ToUniversalTime instead
Deprecate AsNullableDateTime: use ToNullableLocalTime or ToNullableUniversalTime instead
Deprecate AsUniversalTime: use ToUniversalTime instead
Deprecate IsDateTime: use IsValidDateTime instead (aligns with property of the same name in BsonDateTime)