Rethink constraints incorporation

Namely, remove incorporation “otherInsideMyConstraint” to eliminate
constraint system redundancy and produce a potentially very large number
 of constructs.
Instead, introduce not so “spreadable” incorporation during variable
fixation (equality constraint with result type into other constraints).
^KT-41644 Fixed
^KT-42195 Fixed
^KT-42920 Fixed
^KT-42791 Fixed
^KT-41741 Fixed

compiler/testData/diagnostics/testsWithStdLib/inference/performance/kt42195.kt

@@ -0,0 +1,40 @@
+// FIR_IDENTICAL
+
+sealed class Tree<TIndex, out TCommon, out TInner, out TLeaf> {
+    abstract val value: TCommon
+    abstract val children: Map<TIndex, Tree<TIndex, TCommon, TInner, TLeaf>>
+
+    data class Inner<TIndex, TCommon, TInner, TLeaf>(
+        override val value: TCommon,
+        val innerValue: TInner,
+        override val children: Map<TIndex, Tree<TIndex, TCommon, TInner, TLeaf>>
+    ) : Tree<TIndex, TCommon, TInner, TLeaf>()
+
+    data class Leaf<TIndex, TCommon, TLeaf>(
+        override val value: TCommon,
+        val leafValue: TLeaf
+    ) : Tree<TIndex, TCommon, Nothing, TLeaf>() {
+        override val children: Map<TIndex, Tree<TIndex, TCommon, Nothing, TLeaf>> get() = emptyMap()
+    }
+}
+
+val tree = Tree.Inner(
+    "root",
+    Unit,
+    mapOf(
+        1 to Tree.Leaf("1", 1),
+        2 to Tree.Inner(
+            "2",
+            Unit,
+            mapOf(
+                1 to Tree.Leaf("21", 2),
+                2 to Tree.Inner(
+                    "22",
+                    Unit,
+                    mapOf(1 to Tree.Leaf("221", 3))
+                ),
+                3 to Tree.Leaf("23", 4)
+            )
+        )
+    )
+)