[FIR] Implement ASSIGNMENT_TYPE_MISMATCH, RESULT_TYPE_MISMATCH diagnostics, fix tests

compiler/testData/diagnostics/tests/generics/varProjection/setterNotProjectedOutAssign.fir.kt

@@ -5,6 +5,6 @@ interface Tr<T> {
 }
 
 fun test(t: Tr<*>) {
-    t.v = t
+    t.v = <!ASSIGNMENT_TYPE_MISMATCH!>t<!>
     t.v checkType { _<Tr<*>>() }
-}
+}

compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutAssign.fir.kt

@@ -8,7 +8,7 @@ interface Tr<T> {
 
 fun test(t: Tr<*>) {
     t.v = null!!
-    t.v = ""
+    t.v = <!ASSIGNMENT_TYPE_MISMATCH!>""<!>
     t.v = <!NULL_FOR_NONNULL_TYPE!>null<!>
     t.v checkType { _<Any?>() }
-}
+}

compiler/testData/diagnostics/tests/generics/varProjection/setterProjectedOutNoPlusAssign.fir.kt

@@ -7,5 +7,5 @@ interface Tr<T> {
 fun test(t: Tr<out String>) {
     // resolved as t.v = t.v + null!!, where type of right operand is String,
     // so TYPE_MISMATCH: String is not <: of Captured(out String)
-    t.v += null!!
-}
+    <!ASSIGNMENT_TYPE_MISMATCH!>t.v += null!!<!>
+}