launcher: option to run as user without elevation (#695)

## Link to GitHub Issue or related Pull Request, if one exists
#694 

## Description of change
Before this change, we have it set in the executable manifest to always
ask for UAC elevation.

This change removes that and instead attempts to prompt for elevation
when we launch, depending on the new developer option that is being
added here to run as current user instead of elevating.

The default behavior continues to run as admin. This is still the safest
in terms of regression risk.

A bit of history on this: while spicecfg never technically needed to
elevate, we continue to do so to avoid difference in behavior when the
game is launched. For example, if the user is using an input remapper
running without elevation, it would inject input into spicecfg running
as user but fail to do so if the game runs elevated.

WinXP builds are unaffected (there is no UAC).

Some features will straight up fail without elevation so this will
remain as a debug option. To name a few (not a complete list):

* reboot/shutdown of PC
* running at realtime process priority
* `-nvprofile` option
* ...

## Testing

src/spice2x/launcher/launcher.cpp

@@ -5,6 +5,7 @@
 
 #include <assert.h>
 #include <shlwapi.h>
+#include <windows.h>
 #include <cfg/configurator.h>
 
 #include "api/modules/capture.h"
@@ -301,6 +302,26 @@ int main_implementation(int argc, char *argv[]) {
     }
     auto &options = *options_ptr;
 
+#if !SPICE_XP
+
+    {
+        // skip elevation only if AutoElevate is explicitly set to "user"
+        const bool skip_elevation = options[launcher::Options::AutoElevate].is_active() &&
+            options[launcher::Options::AutoElevate].value_text() == "user";
+        if (!skip_elevation && !sysutils::is_running_as_admin()) {
+            log_info("launcher", "relaunching with administrator privileges");
+            if (sysutils::relaunch_as_admin()) {
+                exit(0);
+            } else {
+                // elevation failed or was denied by the user
+                log_fatal("launcher", "failed to launch with administrator privileges");
+                exit(1);
+            }
+        }
+    }
+
+#endif // !SPICE_XP
+
     // check options
     // TODO: get rid of some booleans here and make use of the options directly
     if (options[launcher::Options::OpenConfigurator].value_bool()) {