filesystem: use std for PathExists

Remove custom platform implementation of `PathExists` and replace uses
with `std::filesystem::exists`.

src/xenia/base/filesystem.cc

@@ -17,7 +17,7 @@ namespace filesystem {
 bool CreateParentFolder(const std::filesystem::path& path) {
   if (path.has_parent_path()) {
     auto parent_path = path.parent_path();
-    if (!PathExists(parent_path)) {
+    if (!std::filesystem::exists(parent_path)) {
       return CreateFolder(parent_path);
     }
   }

src/xenia/base/filesystem.h

@@ -36,9 +36,6 @@ std::filesystem::path GetExecutableFolder();
 // Get user folder.
 std::filesystem::path GetUserFolder();
 
-// Returns true of the specified path exists as either a directory or file.
-bool PathExists(const std::filesystem::path& path);
-
 // Creates the parent folder of the specified path if needed.
 // This can be used to ensure the destination path for a new file exists before
 // attempting to create it.

src/xenia/base/filesystem_posix.cc

@@ -77,11 +77,6 @@ std::filesystem::path GetUserFolder() {
   return std::filesystem::path(home) / ".local" / "share";
 }
 
-bool PathExists(const std::filesystem::path& path) {
-  struct stat st;
-  return stat(path.c_str(), &st) == 0;
-}
-
 FILE* OpenFile(const std::filesystem::path& path, const std::string_view mode) {
   return fopen(path.c_str(), std::string(mode).c_str());
 }

src/xenia/base/filesystem_win.cc

@@ -61,18 +61,13 @@ std::filesystem::path GetUserFolder() {
   return result;
 }
 
-bool PathExists(const std::filesystem::path& path) {
-  DWORD attrib = GetFileAttributes(path.c_str());
-  return attrib != INVALID_FILE_ATTRIBUTES;
-}
-
 bool CreateFolder(const std::filesystem::path& path) {
   std::filesystem::path create_path;
   for (auto it = path.begin(); it != path.end(); ++it) {
     create_path /= *it;
     CreateDirectoryW(create_path.c_str(), nullptr);
   }
-  return PathExists(path);
+  return std::filesystem::exists(path);
 }
 
 bool DeleteFolder(const std::filesystem::path& path) {