feat(cli): Load save and replay files from absolute paths

[bobtista]

• Closes Allow -loadsave and -loadreplay to load files from any directory #3078
• Depends on feat(cli): Add -loadsave option #3001, whose commits are included here until it merges

-loadsave and -loadreplay resolve their argument inside the managed user Save and Replays directories, so a file anywhere else has to be copied in before it can be opened. That rules out launching the game directly for a .sav or .rep from an operating-system file handler.

Now an absolute path is opened in place while a relative name still resolves from its managed directory, so both forms keep working. FileSystem::isAbsolutePath classifies the argument - a drive root (C:\, C:/), a current-drive or UNC root (leading separator), or a POSIX root - and GameState::getSaveGamePathForRead returns the path untouched when it is absolute. Save writes and the save menu are unaffected; they continue to use the managed directory.

-loadreplay is added alongside the existing -replay so an externally supplied replay goes through normal Replay synchronization handling. Suppressing synchronization errors stays opt-in through -ignoreReplaySyncErrors rather than being implied by loading from a path.

Command-line saves and replays are now also validated and deferred until the client has initialized the shell, so a bad path reports cleanly instead of failing partway into startup.

Verified on Windows against a clean upstream data set, with a bogus path as a control so a pass
is distinguishable from "the game started anyway":

case	result
control: bogus absolute path	exits
Save from an absolute path outside the user directory	loads
Save from an absolute path containing spaces (quoted)	loads
Save from a UNC path (\\localhost\C$\...)	loads
Relative Save filename	loads from the managed directory
Replay from an absolute path outside the user directory	loads and plays
Replay from an absolute path containing spaces (quoted)	loads and plays
Relative Replay filename	loads from the managed directory
Normal Replay synchronization reporting	reports normally (InGame:C337AE46 Replay:7FB5DE80)

Paths containing spaces work when quoted, which is the form an operating-system file handler
passes. nextParam is quote-aware: a token beginning with " terminates on the next " rather
than on whitespace, so the spaces inside are preserved.

Todo:

• Both games build (z_generals and g_generals, 1458/1458)
• Absolute path classification covers drive roots, UNC and current-drive roots, and POSIX roots
• Save and Replay paths outside the user data directory
• Paths containing spaces
• Windows drive and UNC paths
• Relative Save and Replay filenames still resolve from the managed directories
• Normal Replay synchronization reporting
• macOS and Linux absolute paths
• Restarting an externally loaded Replay
• -ignoreReplaySyncErrors