CFE: optional super-initializer parameters inherit default values incorrectly

[alexmarkov]

This is a part of #47525.

co19/LanguageFeatures/Super-parameters/semantics_A06_t10 test fails with RuntimeError on the VM because default values of super-parameters are incorrect.

class S {
  int s1;
  int s2;
  S(this.s1, [this.s2 = 42]);
}

class C extends S {
  int i1;
  int i2;
  C(this.i1, super.s1, int x, [super.s2]) : this.i2 = x;
}

Kernel:

  class S extends core::Object {
    field core::int s1;
    field core::int s2;
    constructor •(core::int s1, [core::int s2 = #C1]) → sem::S
      : sem::S::s1 = s1, sem::S::s2 = s2, super core::Object::•()
      ;
  }
  class C extends sem::S {
    field core::int i1;
    field core::int i2;
    constructor •(core::int i1 = #C1, core::int s1, core::int x, [core::int s2 = #C2]) → sem::C
      : sem::C::i1 = i1, sem::C::i2 = x, super sem::S::•(s1, s2)
      ;
  }

  #C1 = 42
  #C2 = null

Here s2 parameter in C should have a default value #C1 (42), but it has a default value #C2 (null). Parameter i1 is not optional, so it shouldn't have a default value at all.

/cc @johnniwinther @chloestefantsova

[alexmarkov]

co19/LanguageFeatures/Super-parameters/summary_A04_t01, co19/LanguageFeatures/Super-parameters/summary_A04_t02 and co19/LanguageFeatures/Super-parameters/type_inference_A05_t01 also fail with RuntimeError due to this bug.

[chloestefantsova]

Thanks for spotting that! I'm working on a fix at https://dart-review.googlesource.com/c/sdk/+/228204.