constructor.name of a generic-class instance reports the mangled specialization (Gen$num), not Gen #7632

(new Gen<number>()).constructor.name reports the MANGLED specialization name
Gen$num where node reports Gen.

Repro

class Base {}
class Gen<T> extends Base {}
class GenNoExtends<T> {}

const a = new Gen<number>();
const b = new Gen();               // no type arguments
const c = new GenNoExtends<number>();
console.log(a.constructor.name, b.constructor.name, c.constructor.name);

$ node --experimental-strip-types t.ts
Gen Gen GenNoExtends

$ ./t
Gen$num Gen GenNoExtends$num

Only the instantiation WITH type arguments is affected — that is the one that
gets monomorphized.

Same root cause as #7575, different surface

Perry specializes generic classes: new Gen<number>() emits a second class named
Gen$num (crates/perry-hir/src/monomorph/mangle.rs,
generate_specialized_name) and constructs THAT. #7575 (PR #7631) fixed the
instanceof half by recording Class::specialized_from in the HIR and teaching
the instanceof chain walk a specialization→generic edge. The user-visible class
NAME is the other half of the same leak, and was deliberately left out of that
PR: it flows through the class display-name registry rather than the class-id
chain, and it can change error-message text (TypeError: ... is not a constructor, Object.prototype.toString, stack frames), so it wants its own
parity sweep rather than being bundled into an instanceof fix.

Class::specialized_from already carries what is needed (Some("Gen") on the
specialization), so the likely shape is to register the ORIGIN name as the
class's display name — the class_display_names mechanism in
crates/perry-codegen/src/codegen/string_pool.rs already exists for #5592's
uniquified class-expression bindings.

Worth checking in the same pass

• Gen.name read off the constructor itself, not an instance.
• Object.prototype.toString.call(new Gen<number>()).
• Error subclasses: class MyErr<T> extends Error {} — err.name and the
  toString() prefix.
• Whether any diagnostic or --print-hir/--trace output is keyed on the
  mangled name and would become ambiguous if two specializations both report
  Gen.