Update Array.xml change ArgumentOutOfRangeException description for 'startIndex' parameter on FindIndex methods (#9720)

Changed it to match String.Substring, because the behavior is identical (and original description is arguably wrong or hard to understand).

Fixes: #9719

Author: Fast-Nick

xml/System/Array.xml

@@ -3825,7 +3825,7 @@
 
  <paramref name="match" /> is <see langword="null" />.</exception>
         <exception cref="T:System.ArgumentOutOfRangeException">
-          <paramref name="startIndex" /> is outside the range of valid indexes for <paramref name="array" />.</exception>
+          <paramref name="startIndex" /> is less than zero or greater than the length of the <paramref name="array" />.</exception>
         <altmember cref="M:System.Array.Exists``1(``0[],System.Predicate{``0})" />
         <altmember cref="M:System.Array.Find``1(``0[],System.Predicate{``0})" />
         <altmember cref="M:System.Array.FindLast``1(``0[],System.Predicate{``0})" />
@@ -3917,7 +3917,7 @@
 
  <paramref name="match" /> is <see langword="null" />.</exception>
         <exception cref="T:System.ArgumentOutOfRangeException">
-          <paramref name="startIndex" /> is outside the range of valid indexes for <paramref name="array" />.
+          <paramref name="startIndex" /> is less than zero or greater than the length of the <paramref name="array" />.
 
  -or-