Optimize DirectIOIndexInput

[ChrisHegarty]

This issue has been filed to track various low-level optimisations to the DirectIOIndexInput.

A few specific points:

• add overloads for primitive access, getShort, getInt, etc. DirectIOIndexInput - add overloads for primitive access #14107
• add overloads for bulk retrieval, e.g. readInts(int[] dst, int offset, int len) DirectIOIndexInput - add overloads for bulk retrieval #14124
• avoid double buffering with BufferedIndexInput Avoid double buffering direct IO index input slices with BufferedIndexInput #14103