cmake: extend integration tests

- ci/GHA: add cmake integration tests for Windows.
- ci/GHA: test `add_subdirectory` with Libgcrypt.
- make them run faster with prefill, unity, Ninja, omitting curl tool.
- add support for any build configuration.
- add old-cmake support with auto-detection.
- auto-detect Ninja.
- run consumer test apps to see if they work.
  Also show the cryptography backend.
- add support for Windows.
- make it more verbose.
- re-add `ExternalProject` cmake consumer test. It's broken.
- tidy up terminology.

Cherry-picked from #1581

Closes #1589

tests/cmake/test.c

@@ -6,8 +6,34 @@
 #include "libssh2.h"
 #include <stdio.h>
 
-int main(void)
+int main(int argc, char **argv)
 {
-    printf("libssh2_version(0): |%s|\n", libssh2_version(0));
+    const char *crypto_str;
+
+    (void)argc;
+
+    switch(libssh2_crypto_engine()) {
+    case libssh2_gcrypt:
+        crypto_str = "libgcrypt";
+        break;
+    case libssh2_mbedtls:
+        crypto_str = "mbedTLS";
+        break;
+    case libssh2_openssl:
+        crypto_str = "openssl compatible";
+        break;
+    case libssh2_os400qc3:
+        crypto_str = "OS400QC3";
+        break;
+    case libssh2_wincng:
+        crypto_str = "WinCNG";
+        break;
+    default:
+        crypto_str = "(unrecognized)";
+    }
+
+    printf("libssh2 test: |%s|%s|%s|\n", argv[0],
+                                         libssh2_version(0), crypto_str);
+
     return 0;
 }