Snake case naming convention causes incorrect table names for TPH hierarchies

[benlongo]

Cross-posting this from ef core repo: dotnet/efcore#35604

Repro:

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;

await using var ctx = new MyContext();
await ctx.Database.EnsureDeletedAsync();
await ctx.Database.EnsureCreatedAsync();

Console.WriteLine( "With instantiated DbContext:" );
foreach( var et in ctx.Model.GetEntityTypes() ) {
    var tn = et.GetTableName();
    Console.WriteLine( $"{et.ClrType.Name} -> {tn}" );
}

public class MyContext : DbContext {
    public DbSet<MyEntity> Entities { get; set; }

    protected override void OnModelCreating( ModelBuilder modelBuilder ) {
        modelBuilder.Entity<MyEntity>()
            .HasDiscriminator<string>( "entity_type" )
            .HasValue<MyDerivedEntity1>( "1" )
            .HasValue<MyDerivedEntity2>( "2" );

        modelBuilder.Entity<MyEntity>()
            .ToTable( "entity_table" );

        modelBuilder.Entity<MyDerivedEntity1>()
            .HasBaseType<MyEntity>();

        modelBuilder.Entity<MyDerivedEntity2>()
            .HasBaseType<MyEntity>();

        Console.WriteLine( "Within OnModelCreating:" );
        foreach( IMutableEntityType mutableEntityType in modelBuilder.Model.GetEntityTypes() ) {
            var tableName = mutableEntityType.GetTableName();
            Console.WriteLine( $"{mutableEntityType.ClrType.Name} -> {tableName}" );
        }
    }

    protected override void OnConfiguring( DbContextOptionsBuilder optionsBuilder ) {
        optionsBuilder
            .UseSqlite( "DataSource=:memory:" )
            .EnableSensitiveDataLogging()
            .UseSnakeCaseNamingConvention();
    }
}

public abstract class MyEntity {
    public int Id { get; set; }
    public string Shared { get; set; }
}

public class MyDerivedEntity1 : MyEntity {
    public string Foo { get; set; }
}

public class MyDerivedEntity2 : MyEntity {
    public string Bar { get; set; }
}

Output:

Within OnModelCreating:
MyDerivedEntity1 -> entities
MyDerivedEntity2 -> entities
MyEntity -> entity_table
Within OnModelCreating:
MyDerivedEntity1 -> entities
MyDerivedEntity2 -> entities
MyEntity -> entity_table
With instantiated DbContext:
MyDerivedEntity1 -> entity_table
MyDerivedEntity2 -> entity_table
MyEntity -> entity_table