loader: Add extension before CreateInstance chain

A developer can cause the loader to enable VK_EXT_debug_report
extension by setting a specific property. However, that check
was happening after the instance chain was called and thus
no layers saw the extension enabled.
Also fix use of AddExtensionToCreateInfo to always allocate
and insert VK_EXT_debug_report. Otherwise cannot distinguish
between the failure case and the extension is already present
case.

Change-Id: Id64bb14cb2086e94190625b4364329d634afda70