FIR checker: warn unnecessary non-null assertions

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.fir.kt

@@ -6,7 +6,7 @@ interface G {
 }
 
 fun foo1(a: Int?, b: G) {
-    b[a!!, a!!] = a
+    b[a!!, a<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>] = a
     checkSubtype<Int>(a)
 }
 

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayIndices.fir.kt

@@ -1,7 +1,7 @@
 // !CHECK_TYPE
 
 fun foo1(a: Int?, b: Array<Array<Int>>) {
-    b[a!!][a!!] = a
+    b[a!!][a<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>] = a
     checkSubtype<Int>(a)
 }
 

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ExclExcl.fir.kt

@@ -2,7 +2,7 @@ fun bar(x: Int) = x + 1
 
 fun f1(x: Int?) {
     <!INAPPLICABLE_CANDIDATE!>bar<!>(x)
-    if (x != null) bar(x!!)
+    if (x != null) bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
     if (x == null) bar(x!!)
 }
 
@@ -11,13 +11,13 @@ fun f2(x: Int?) {
 }
 
 fun f3(x: Int?) {    
-    if (x != null) bar(x!!) else x!!
+    if (x != null) bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>) else x!!
 }
     
 fun f4(x: Int?) {    
-    if (x == null) x!! else bar(x!!)
+    if (x == null) x!! else bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
 }
 
 fun f5(x: Int?) {    
-    if (x == null) else bar(x!!)
+    if (x == null) else bar(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
 }

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/IfThenElse.fir.kt

@@ -26,5 +26,5 @@ fun foo() {
     if (z != null) bar(z)
     <!INAPPLICABLE_CANDIDATE!>bar<!>(z)
     bar(z!!)
-    if (z != null) bar(z!!)
+    if (z != null) bar(z<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
 }