Add Table-Valued function support to EntityMapping.

[Freydoonk]

TableValuedFunction supporting was added.
To did this the EntityMapping class was converted to an abstract class. TableValuedFunctionEntityMapping and EntityMapping which inherited the abstract EntityMapping were added.

SetDatabseName was addedd to EntityMapping configuration options.
A new facility was added to specify a Database name to each entity while doing configuration.

[MoonStorm]

Thanks for sharing your work. I'm gonna try to find some time to review it. I have a couple of ideas myself to refactor the JOINs. We'll see what comes out.

[iamteamstar]

one commit, a lot of change. few files, not healtly

[iamteamstar]

please dont attribute in entity class. you can configuration class for this constraints. for examle
public void Configure(EntityTypeBuilder builder)
{
builder.ToTable("Students");

	builder.HasKey(x => x.ID);

	builder.Property(x => x.Name)
		   .IsRequired()
		   .HasMaxLength(50);

	builder.Property(x => x.Email)
		   .IsRequired()
		   .HasMaxLength(100);

	builder.HasCheckConstraint("CK_Student_Email", "[Email] LIKE '%@%.%'");

	builder.Property(x => x.TCNo)
		   .IsRequired()
		   .HasMaxLength(11)
		   .IsFixedLength();

	builder.HasCheckConstraint("CK_Student_TCNo", "LEN([TCNo]) = 11 AND [TCNo] NOT LIKE '%[^0-9]%'");

	builder.HasIndex(x => x.Email).IsUnique();
}

(you need implemet IEntityTypeConfiguration interface)