Add Crusader-specific USECODE data and documentation

- Introduced new file `vm_mask_ladder.tsv` containing detailed mappings for Crusader USECODE VM masks and their associated descriptors.
- Added comprehensive documentation in `scummvm-crusader-reference.md` outlining the structure, findings, and implications for reverse-engineering the Crusader engine within ScummVM.
- Created `usecode-roundtrip-ir.md` to document the plan for converting Crusader USECODE bytes into a human-readable format, detailing the container layout, event names, and intrinsic tables.
- Implemented a PowerShell script `temp_usecode_sample.ps1` for extracting and analyzing USECODE data from the Crusader FLX files, providing insights into class and event structures.

Crusader.rep/user/~index.dat

@@ -1,11 +1,12 @@
 VERSION=1
 /
   00000006:udf_c0a86451f2583322595358500:c0a86451c1883616844258300
+  00000007:udf_c0a86451fc492611033559300:c0a86451cb1215992032385300
   00000002:udf_c0a8647bd82013090643707800:c0a8647bd36436342237796300
   00000004:udf_c0a8647bdaf715949048416300:c0a8647bd36636342258818700
   00000005:udf_c0a8647bdba516037949612600:c0a8647bd36736342281220400
   00000000:udf_c0a8647bf0178892741854800:c0a8647bd36236342207469100
   00000001:udf_c0a8647bf4b212984786819600:c0a8647bd36336342224113900
   00000003:udf_c0a8647bfe7615910786193500:c0a8647bd36536342248279100
-NEXT-ID:7
+NEXT-ID:8
 MD5:d41d8cd98f00b204e9800998ecf8427e

Crusader.rep/user/~journal.dat

@@ -1,2 +0,0 @@
-IADD:00000007:/udf_c0a86451fc492611033559300
-IDSET:/udf_c0a86451fc492611033559300:c0a86451cb1215992032385300