Support "long format" DLL import libraries

[HertzDevil]

Crystal::System::LibraryArchive.imported_dlls is used by the interpreter to obtain all dependent DLLs of a given import library. Currently, the method only supports libraries using the short format, emitted by MSVC's linker. This PR implements the long format used by MinGW-w64 when passing the -Wl,--out-implib flag to cc.

Specs will be added when Crystal::Loader supports MinGW-w64. In the mean time, if you have MSYS2, you could try this on the UCRT64 import libraries:

require "crystal/system/win32/library_archive"

Crystal::System::LibraryArchive.imported_dlls("C:/msys64/ucrt64/lib/libpcre2-8.dll.a") # => Set{"libpcre2-8-0.dll"}
Crystal::System::LibraryArchive.imported_dlls("C:/msys64/ucrt64/lib/libucrt.a")        # => Set{"api-ms-win-crt-utility-l1-1-0.dll", "api-ms-win-crt-time-l1-1-0.dll", "api-ms-win-crt-string-l1-1-0.dll", "api-ms-win-crt-stdio-l1-1-0.dll", "api-ms-win-crt-runtime-l1-1-0.dll", "api-ms-win-crt-process-l1-1-0.dll", "api-ms-win-crt-private-l1-1-0.dll", "api-ms-win-crt-multibyte-l1-1-0.dll", "api-ms-win-crt-math-l1-1-0.dll", "api-ms-win-crt-locale-l1-1-0.dll", "api-ms-win-crt-heap-l1-1-0.dll", "api-ms-win-crt-filesystem-l1-1-0.dll", "api-ms-win-crt-environment-l1-1-0.dll", "api-ms-win-crt-convert-l1-1-0.dll", "api-ms-win-crt-conio-l1-1-0.dll"}