windows: fix UWP builds, add GHA job

Add new job to test building for UWP (aka `CURL_WINDOWS_APP`).

Fix fallouts when building for UWP:
- rand: do not use `BCryptGenRandom()`.
- cmake: disable using win32 LDAP.
- cmake: disable telnet.
- version_win32: fix code before declaration.
- schannel: disable `HAS_MANUAL_VERIFY_API`.
- schannel: disable `SSLSUPP_PINNEDPUBKEY`
  and make `schannel_checksum()` a stub.
  Ref: e178fbd40a #1429
- schannel: make `cert_get_name_string()` a failing stub.
- system_win32: make `Curl_win32_impersonating()` a failing stub.
- system_win32: try to fix `Curl_win32_init()` (untested).
- threads: fix to use `CreateThread()`.
- src: disable searching `PATH` for the CA bundle.
- src: disable bold text support and capability detection.
- src: disable `getfiletime()`/`setfiletime()`.
- tests: make `win32_load_system_library()` a failing stub.
- tests/server/util: make it compile.
- tests/server/sockfilt: make it compile.
- tests/lib3026: fix to use `CreateThread()`.

See individual commits for build error details.

Some of these fixes may have better solutions, and some may not work
as expected. The goal of this patch is to make curl build for UWP.

Closes #13870

lib/asyn-thread.c

@@ -459,7 +459,7 @@ query_complete(DWORD err, DWORD bytes, LPWSAOVERLAPPED overlapped)
  * and wait on it.
  */
 static
-#if defined(_WIN32_WCE)
+#if defined(_WIN32_WCE) || defined(CURL_WINDOWS_APP)
 DWORD
 #else
 unsigned int
@@ -527,7 +527,7 @@ CURL_STDCALL getaddrinfo_thread(void *arg)
  * gethostbyname_thread() resolves a name and then exits.
  */
 static
-#if defined(_WIN32_WCE)
+#if defined(_WIN32_WCE) || defined(CURL_WINDOWS_APP)
 DWORD
 #else
 unsigned int