CLI: improve diagnostic message format

- render the whole line where the error/warning points to, if any, and another
  line with '^', like other compilers do
- lowercase diagnostic severity
- decapitalize the message if it doesn't start with a proper name

compiler/testData/cli/js/diagnosticWhenReferenceToBuiltinsMember.out

@@ -1,3 +1,7 @@
-ERROR: compiler/testData/cli/js/diagnosticWhenReferenceToBuiltinsMember.kt: (4, 5) Callable references for builtin members are not supported yet: 'Int::toByte'
-ERROR: compiler/testData/cli/js/diagnosticWhenReferenceToBuiltinsMember.kt: (5, 5) Callable references for builtin members are not supported yet: 'String::length'
+compiler/testData/cli/js/diagnosticWhenReferenceToBuiltinsMember.kt:4:5: error: callable references for builtin members are not supported yet: 'Int::toByte'
+    Int::toByte
+    ^
+compiler/testData/cli/js/diagnosticWhenReferenceToBuiltinsMember.kt:5:5: error: callable references for builtin members are not supported yet: 'String::length'
+    String::length
+    ^
 COMPILATION_ERROR