FIR checker: differentiate UNSAFE_CALL from INAPPLICABLE_CANDIDATE

To do so, inside the root cause of inapplicable candidate errors,
we will record expected/actual type of receiver, if any.
That will help identifying inapplicable calls on nullable receiver.

compiler/testData/diagnostics/testsWithStdLib/tryCatch/assignTry.fir.kt

@@ -15,7 +15,7 @@ fun test2() {
     catch (e: ExcB) {
         10
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test3() {
@@ -28,7 +28,7 @@ fun test3() {
     catch (e: ExcB) {
         return
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test4() {
@@ -41,7 +41,7 @@ fun test4() {
     finally {
         ""
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test5() {
@@ -54,7 +54,7 @@ fun test5() {
     finally {
         return
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test6() {
@@ -67,7 +67,7 @@ fun test6() {
     catch (e: ExcB) {
         return
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test7() {
@@ -80,7 +80,7 @@ fun test7() {
     catch (e: ExcB) {
         ""
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test8() {
@@ -89,7 +89,7 @@ fun test8() {
     } catch (e: ExcA) {
         null
     }
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.<!UNSAFE_CALL!>length<!>
 }
 
 fun test9() {