Create process with wide chars on Windows

Windows does not support UTF-8, so pushing a file with non-ASCII
characters failed.

Convert the UTF-8 command line to a wide characters string and call
CreateProcessW().

Fixes <https://github.com/Genymobile/scrcpy/issues/422>

app/src/str_util.c

@@ -3,6 +3,11 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifdef _WIN32
+# include <windows.h>
+# include <tchar.h>
+#endif
+
 size_t xstrncpy(char *dest, const char *src, size_t n) {
     size_t i;
     for (i = 0; i < n - 1 && src[i] != '\0'; ++i)
@@ -47,3 +52,22 @@ char *strquote(const char *src) {
     quoted[len + 2] = '\0';
     return quoted;
 }
+
+#ifdef _WIN32
+
+wchar_t *utf8_to_wide_char(const char *utf8) {
+    int len = MultiByteToWideChar(CP_UTF8, 0, utf8, -1, NULL, 0);
+    if (!len) {
+        return NULL;
+    }
+
+    wchar_t *wide = malloc(len * sizeof(wchar_t));
+    if (!wide) {
+        return NULL;
+    }
+
+    MultiByteToWideChar(CP_UTF8, 0, utf8, -1, wide, len);
+    return wide;
+}
+
+#endif