[lldb][NFC] Move generic DWARFASTParser code out of Clang-specific code

This patch moves ParseChildArrayInfo out of DWARFASTParserClang in order
to decouple Clang-specific logic from DWARFASTParser.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D114668



Signed-off-by: Luís Ferreira <contact@lsferreira.net>