K2: Fix generic inference case with !! synthetic call

Result of the `checkNotNull` calls should always be a non-nullable
values.
The simplest idea how to acheive it is adding not-nullable Any bound
to the type parameter declaration.

Existing comment stating about impossibility of such bound seems to be
not 100% correct because it doesn't take into account presence of
definitely-non-nullable X & Any types that allow described case with
nullable generic.

^KT-55804 Fixed

compiler/testData/diagnostics/tests/inference/exclExclInference.fir.kt

@@ -0,0 +1,17 @@
+// FIR_DUMP
+// ISSUE: KT-55804
+
+fun foo() {
+    val x: String?
+    x = materialize()!! // Should be treated as non-nullable assignment
+    x.length // Should be allowed
+}
+
+fun <E> materialize(): E = TODO()
+
+fun <F> test(f: F) = f!!
+
+fun main() {
+    test<String>("").length
+    test<String?>(null).length // `.length` should be allowed because return type of "test" should be inferred to `F & Any`
+}

compiler/testData/diagnostics/tests/inference/exclExclInference.fir.txt

@@ -0,0 +1,16 @@
+FILE: exclExclInference.fir.kt
+    public final fun foo(): R|kotlin/Unit| {
+        lval x: R|kotlin/String?|
+        R|<local>/x| = R|/materialize|<R|kotlin/String?|>()!!
+        R|<local>/x|.R|kotlin/String.length|
+    }
+    public final fun <E> materialize(): R|E| {
+        ^materialize R|kotlin/TODO|()
+    }
+    public final fun <F> test(f: R|F|): R|F & Any| {
+        ^test R|<local>/f|!!
+    }
+    public final fun main(): R|kotlin/Unit| {
+        R|/test|<R|kotlin/String|>(String()).R|kotlin/String.length|
+        R|/test|<R|kotlin/String?|>(Null(null)).R|kotlin/String.length|
+    }

compiler/testData/diagnostics/tests/inference/exclExclInference.kt

@@ -0,0 +1,17 @@
+// FIR_DUMP
+// ISSUE: KT-55804
+
+fun foo() {
+    val x: String?
+    x = materialize()!! // Should be treated as non-nullable assignment
+    <!DEBUG_INFO_SMARTCAST!>x<!>.length // Should be allowed
+}
+
+fun <E> materialize(): E = TODO()
+
+fun <F> test(f: F) = f!!
+
+fun main() {
+    test<String>("").length
+    test<String?>(null).length // `.length` should be allowed because return type of "test" should be inferred to `F & Any`
+}

compiler/testData/diagnostics/tests/inference/regressions/kt36342.fir.kt

@@ -4,8 +4,8 @@ import java.lang.Exception
 fun <K> id(arg: K): K = arg
 
 fun test() {
-    <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>id(<!UNRESOLVED_REFERENCE!>unresolved<!>)!!<!>
-    <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!><!UNRESOLVED_REFERENCE!>unresolved<!>!!!!<!>
+    id(<!UNRESOLVED_REFERENCE!>unresolved<!>)!!
+    <!UNRESOLVED_REFERENCE!>unresolved<!>!!<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>
     <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>try {
         id(<!UNRESOLVED_REFERENCE!>unresolved<!>)
     } catch (e: Exception) {