Minimally fix the known unsoundness in bevy_mikktspace (#5299)

# Objective

- 0.8 is coming soon, and our mikktspace implementation is unsound - see gltf-rs/mikktspace#26
- Best not to ship that

## Solution

- Fix the unsoundness in a minimal way
- Obviously there might be others, but it seems unlikely we have any way to know about those

Author: DJMcNab

crates/bevy_mikktspace/src/generated.rs

@@ -1060,8 +1060,8 @@ unsafe fn InitTriInfo<I: Geometry>(
                     let mut bChooseOrientFirstTri: bool = false;
                     if (*pTriInfos.offset((t + 1) as isize)).iFlag & 4i32 != 0i32 {
                         bChooseOrientFirstTri = true
-                    } else if CalcTexArea(geometry, &*piTriListIn.offset((t * 3 + 0) as isize))
-                        >= CalcTexArea(geometry, &*piTriListIn.offset(((t + 1) * 3 + 0) as isize))
+                    } else if CalcTexArea(geometry, piTriListIn.offset((t * 3 + 0) as isize))
+                        >= CalcTexArea(geometry, piTriListIn.offset(((t + 1) * 3 + 0) as isize))
                     {
                         bChooseOrientFirstTri = true
                     }
@@ -1503,9 +1503,7 @@ unsafe fn GenerateSharedVerticesIndexList<I: Geometry>(
             vP_1.z
         };
         let iCell_0 = FindGridCell(fMin, fMax, fVal_0);
-        let mut pTable: *mut i32 = 0 as *mut i32;
-        pTable = &mut piHashTable[piHashOffsets[iCell_0] as usize] as *mut i32;
-        *pTable.offset(piHashCount2[iCell_0] as isize) = i as i32;
+        piHashTable[(piHashOffsets[iCell_0] + piHashCount2[iCell_0]) as usize] = i as i32;
         piHashCount2[iCell_0] += 1;
         i += 1
     }
@@ -1525,7 +1523,7 @@ unsafe fn GenerateSharedVerticesIndexList<I: Geometry>(
     k = 0;
     while k < g_iCells {
         // extract table of cell k and amount of entries in it
-        let mut pTable_0 = &mut piHashTable[piHashOffsets[k] as usize] as *mut i32;
+        let pTable_0 = piHashTable.as_mut_ptr().offset(piHashOffsets[k] as isize);
         let iEntries = piHashCount[k] as usize;
         if !(iEntries < 2) {
             e = 0;