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/testData/diagnostics/tests/extensions/throwOutCandidatesByReceiver.fir.kt

@@ -8,7 +8,7 @@ fun <R> List<R>.a() {}
 
 fun test1(i: Int?) {
     1.<!INAPPLICABLE_CANDIDATE!>a<!>()
-    i<!UNSAFE_CALL!>.<!>a()
+    i.<!INAPPLICABLE_CANDIDATE!>a<!>()
 }
 
 fun <R> test2(c: Collection<R>) {
@@ -19,7 +19,7 @@ fun Int.foo() {}
 
 fun test3(s: String?) {
     "".<!INAPPLICABLE_CANDIDATE!>foo<!>()
-    s<!UNSAFE_CALL!>.<!>foo()
+    s.<!INAPPLICABLE_CANDIDATE!>foo<!>()
     "".foo(<!TOO_MANY_ARGUMENTS!>1<!>)
     s.foo(<!TOO_MANY_ARGUMENTS!>"a"<!>)
 }
@@ -52,5 +52,5 @@ fun test7(l: List<String?>) {
 }
 
 fun test8(l: List<Any>?) {
-    l<!UNSAFE_CALL!>.<!>b()
+    l.<!INAPPLICABLE_CANDIDATE!>b<!>()
 }