Refactor resolution of double colon expression LHS

Try resolving the LHS only when it looks (PSI-wise) like it could represent a
type element. This, for example, allows "illegal selector" error to be reported
on weird expressions like '""?.""::class'.

Also remove expression text from the "illegal selector" diagnostic, it's not
needed and can screw up the error message if the text is too big

compiler/testData/diagnostics/tests/incompleteCode/illegalSelectorCallableReference.kt

@@ -0,0 +1,8 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION
+
+fun test() {
+    "a".<!ILLEGAL_SELECTOR!>"b"<!>::<!UNRESOLVED_REFERENCE!>foo<!>
+    "a".<!ILLEGAL_SELECTOR!>"b"<!>::class
+    "a".<!ILLEGAL_SELECTOR!>"b"<!>.<!ILLEGAL_SELECTOR!>"c"<!>::<!UNRESOLVED_REFERENCE!>foo<!>
+    "a".<!ILLEGAL_SELECTOR!>"b"<!>.<!ILLEGAL_SELECTOR!>"c"<!>::class
+}

compiler/testData/diagnostics/tests/incompleteCode/illegalSelectorCallableReference.txt

@@ -0,0 +1,3 @@
+package
+
+public fun test(): kotlin.Unit