Streamless implementation. It's ~ 2x faster for small files.
getInputStreamAsCharArray is a hotspot during
CompilationUnit.getContents().

Change-Id: I7daf60e52cbc34997ba24164285f769f604cc515
Signed-off-by: Joerg Kubitz <jkubitz-eclipse@gmx.de>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.core/+/178470
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Manoj Palat <manpalat@in.ibm.com>