Improve SkipNBytes to RandomInputStream (#14557)

* Convert SkipNBytes in InputStreamInterface to pure virtual

This fix tries to address the issue raised in 14512 where SkipNBytes
will takes a long time as it needs to read through the file
even though it is possible to random access.

This fix convert SkipNBytes in InputStreamInterface to pure virtual
so that it is possible to have different implementations based
on the underlying file type (seekable vs. no seekable)

This fix fixes 14512.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add missing implementation in inputstream_interface_test.cc

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update implementation of RandomInputStream

So that if random access read of 1 byte to the expected pos
is able to complete then return immediately. Otherwise,
read through until the pos is reached.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add SkipNBytes to SnappyInputBuffer

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove inputstream_interface.cc from makefile

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove pure virtual and use override for RandomInputStream

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>