FIR: add UnsafeCall resolution diagnostics

Previously unsafe call is reported as part of InapplicableWrongReceiver.
This makes it difficult for the downstream checkers to report different
diagnostics.

compiler/fir/analysis-tests/testData/resolve/smartcasts/variables/delayedAssignment.dot

@@ -77,7 +77,7 @@ digraph delayedAssignment_kt {
                 32 [label="Exit when"];
             }
             33 [label="Access variable R|<local>/a|"];
-            34 [label="Function call: R|<local>/a|.<Inapplicable(INAPPLICABLE_WRONG_RECEIVER): /A.foo>#()"];
+            34 [label="Function call: R|<local>/a|.<Inapplicable(UNSAFE_CALL): /A.foo>#()"];
             35 [label="Exit block"];
         }
         36 [label="Exit function test" style="filled" fillcolor=red];