FIR checker: report unresolved reference in imports

Compared to FE1.0, instead of using UNRESOLVED_REFERENCE, a new
UNRESOLVED_IMPORT diagnostic is introduced. This is so that we can use a
different positioning strategy to highlight the last part of the import
if the entire import is passed.

Also, this change fixed some incorrectly rejected imports in FIR. Such
cases are covered the newly added test file staticFunAndPropertyImport.kt

compiler/testData/diagnostics/tests/regressions/kt762.fir.kt

@@ -1,4 +1,4 @@
 //KT-762 Wrong highlighting in imports (No errors reported on unresolved imports)
-import aaa // must be an error
+import <!UNRESOLVED_IMPORT!>aaa<!> // must be an error
 
 fun main() {}