Add documentation for LowerBound in ArrayItems

This PR adds in the documentation for the existing LowerBound element in
ArrayItems for C++ Natvis.

Author: WardenGnaw

docs/debugger/create-custom-views-of-native-objects.md

@@ -479,14 +479,19 @@ You can also specify multi-dimensional arrays. In that case, the debugger needs
       <Rank>$T2</Rank>
       <Size>_M_extent._M_base[$i]</Size>
       <ValuePointer>($T1*) _M_buffer_descriptor._M_data_ptr</ValuePointer>
+      <LowerBound>0</LowerBound>
     </ArrayItems>
   </Expand>
 </Type>
 ```
 
 - `Direction` specifies whether the array is in row-major or column-major order.
 - `Rank` specifies the rank of the array.
-- The `Size` element accepts the implicit `$i` parameter, which it substitutes with the dimension index to find the length of the array in that dimension. In the previous example, the expression `_M_extent.M_base[0]` should give the length of the 0th dimension, `_M_extent._M_base[1]` the 1st, and so on.
+- The `Size` element accepts the implicit `$i` parameter, which it substitutes with the dimension index to find the length of the array in that dimension.
+  - In the previous example, the expression `_M_extent.M_base[0]` should give the length of the 0th dimension, `_M_extent._M_base[1]` the 1st, and so on.
+- The `LowerBound` specifies the lower bound of each dimension of the array. For multi-dimensional arrays, you can specify an expression that uses the implicit `$i` parameter. The `$i` parameter will be substituted with the dimension index to find the lower bound of the array in that dimension.
+  - In the previous example, all dimensions will start at 0. However, if you had `($i == 1) ? 1000 : 100` as the lower bound. The 0th dimension will start at 100, and the 1st dimension will start at 1000.
+    - E.g. `[100, 1000], [100, 1001], [100, 1002], ... [101, 1000], [101, 1001],...`
 
 Here's how a two-dimensional `Concurrency::array` object looks in the debugger window: