Allow -loadsave and -loadreplay to load files from any directory

[bobtista]

Depends on #2999
Follow up for #3001

Allow -loadsave <path> and -loadreplay <path> to load .sav and .rep files from any directory during startup without copying them into the user Save or Replays directories.

Absolute paths should be opened in place. Relative filenames should continue to resolve from the expected user directories for backwards compatibility.

-loadreplay should use normal Replay synchronization handling. Diagnostic captures that need to suppress synchronization errors should explicitly use -ignoreReplaySyncErrors.

This enables a later operating-system file handler to launch the game directly for .sav and .rep files.

Compatibility needs testing with:

• Save and Replay paths outside the user data directory
• Paths containing spaces
• Windows drive and UNC paths
• macOS and Linux absolute paths
• Relative Save and Replay filenames
• Restarting an externally loaded Replay
• Normal Replay synchronization reporting
• -ignoreReplaySyncErrors