Fix #37143: Always generate HasDiscriminator with type argument and property name in snapshot

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        Fixes #bugnumber

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Description

Non-string discriminators with the default name "Discriminator" caused spurious migrations on every scaffold because the snapshot omitted the type argument:

// Before (loses type info, defaults to string on read-back)
b.HasDiscriminator().HasValue(0);

// After (preserves int type)
b.HasDiscriminator<int>("Discriminator").HasValue(0);

Changes

• CSharpSnapshotGenerator.cs: Removed && discriminatorProperty.Name != "Discriminator" condition from both entity type and complex property discriminator generation
• Tests: Updated 8 existing baseline tests, added Discriminator_with_non_string_default_name_is_stored_in_snapshot to cover the regression scenario

Fixes #37143

Original prompt

Fix #37143 by always generating a HasDiscriminator call with generic type argument and property name in the snapshot.

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