CONC-447 ERROR 2026 (HY000): SSL connection error: Certificate signature check failed

Implement proper verification for server certificate chain,
with refactoring of the certificate stuff.

If custom CA and CRL certs are given, load them into in-memory store, and
use CertVerifyCertificateChainPolicy() to verify the certificate chain.

There are minor errors fixed, such as
- now there is a support for private keys encoded as BEGIN/END PRIVATE KEY
in PEM, instead of only BEGIN/END RSA PRIVATE KEY
- memory leak around CryptAcquireContext() is fixed i.e when client loads
private key, it previously did never released it, not even when connection
ended.

The handling of certificates moved into schannel_certs.c from various places

libmariadb/win32_errmsg.h

@@ -0,0 +1,2 @@
+#include <windows.h>
+void ma_format_win32_error(char* buf, size_t buflen, DWORD code, _Printf_format_string_ const char* fmt, ...);