Prefer working-directory files in iOS RFile

[tryk016]

Relative paths opened through RFile on iOS are currently resolved only against the application bundle.

This change checks the process working directory first and uses the application bundle as a fallback. Absolute-path behavior remains unchanged, and the change is limited to iOS.

Testing:

• TempestTests on macOS: 174 passed
• iPhoneOS arm64 Release build
• iPhone Simulator arm64 Release build

[Try]

Hm, this is probably undesirable. On PC application can load resources by short paths such as "assets/icon.png". With this PR loading of local data will mostly work like on PC, except if there is a file with the same name in working directory.
Meanwhile, general expectation from application is to always point to external data with fill-path.

[tryk016]

You're right, this could let files from the working directory override bundled resources. I'll fix the OpenGothic call sites to use full paths instead. Thanks!