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/callableReference/packageInLhs.kt

@@ -4,7 +4,7 @@
 package foo
 
 fun test() {
-    <!UNRESOLVED_REFERENCE!>foo<!>::test
+    <!EXPRESSION_EXPECTED_PACKAGE_FOUND!>foo<!>::test
 }
 
 // FILE: qualifiedName.kt
@@ -12,5 +12,5 @@ fun test() {
 package foo.bar
 
 fun test() {
-    foo.<!UNRESOLVED_REFERENCE!>bar<!>::test
+    foo.<!EXPRESSION_EXPECTED_PACKAGE_FOUND!>bar<!>::test
 }