FIR checker: introduce NO_(GET|SET)_METHOD

Besides introducing new diagnostics, this commit unifies source usages
for array accesses in PSI & LT.

compiler/testData/diagnostics/tests/LValueAssignment.fir.kt

@@ -128,7 +128,7 @@ class Test() {
 
         (f@ a)[3] = 4
 
-        <!UNRESOLVED_REFERENCE!>this[54] = 34<!>
+        this<!NO_SET_METHOD!>[54]<!> = 34
     }
 }