Modular installer part1

[IceReaper]

Part 1 #20440
Part 2 #20445
Part 3 #20439

What we have here:

• InstallShield CAB format now also supports version 5. I took the logic from UnShield. Tested to work on KKnD Xtreme demo data1.cab
• ZipFiles are now determined by their zip header, instead of their filename. Otherwise downloaded temp files for example wont be extractable, as they have no file extension.
• And the "biggest" thing here: Installer file sources are now case insensitive. Any game which is released on Windows or MacOS will be case insensitive anyway. This would only lock out pure linux games, which have two identical filenames which only differ in their capitalization. So while theoretically possible, this most likely never occurs as no game dev goes linux only AND uses a filename with different capitalization twice.

[pchote]

A couple of small issues with the latest amendment. I haven't yet had the opportunity to test the installer ingame.

[pchote]

The /./ issue you mentioned in #20439 is a problem here:

On bleed:

Using installer `cnc95: C&C Gold (GDI or Nod Disc, English)` of type `Disc`:
Copying /Volumes/GDI95/./DESERT.MIX -> /Users/paul/Library/Application Support/OpenRA/Content/ra/v2/cnc/desert.mix

On this PR:

Using installer `cnc95: C&C Gold (GDI or Nod Disc, English)` of type `Disc`:
Copying  -> /Users/paul/Library/Application Support/OpenRA/Content/ra/v2/cnc/desert.mix
System.ArgumentNullException: Path cannot be null. (Parameter 'path')
   at System.IO.Strategies.FileStreamHelpers.ValidateArguments(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, Int64 preallocationSize)
   at OpenRA.Mods.Common.Widgets.Logic.InstallFromDiscLogic.<>c__DisplayClass42_0.<InstallFromDisc>b__1() in /Users/paul/src/OpenRA/OpenRA.Mods.Common/Widgets/Logic/Installation/InstallFromDiscLogic.cs:line 286
Deleting /Users/paul/Library/Application Support/OpenRA/Content/ra/v2/cnc/desert.mix

[pchote]

Tested and otherwise works as expected on macOS and Linux, so 👍 once the fix above is applied.

[AspectInteractive2]

The design looks fine. I can't be sure of the installation specifics as this isn't my area of expertise, but as this has been tested successfully and reviewed by pchote I also approve.

[PunkPun]

Merging as approved by both @pchote and @AspectInteractive2

[PunkPun]

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