K2: don't make T = Type! substitutions for constructors, including SAM

Without this commit we get some ABI changes and it looks bad.

Related to KT-65596

compiler/fir/analysis-tests/testData/resolve/problems/flexibleTypeVarAgainstNull.fir.txt

@@ -1,4 +1,4 @@
 FILE: main.kt
     public final fun main(): R|kotlin/Unit| {
-        R|/JavaClass.JavaClass|<R|kotlin/String!|>(Null(null)).R|SubstitutionOverride</JavaClass.foo: R|kotlin/String!|>|().R|kotlin/String.length|
+        R|/JavaClass.JavaClass|<R|kotlin/String|>(Null(null)).R|SubstitutionOverride</JavaClass.foo: R|kotlin/String!|>|().R|kotlin/String.length|
     }