tools: initial implementation of WoA EH decoding
Add support to llvm-readobj to decode Windows ARM Exception Handling data. This
uses the previously added datastructures to decode the information into a format
that can be used by tests. This is a necessary step to add support for emitting
Windows on ARM exception handling information.
A fair amount of formatting inspiration is drawn from the Win64 EH printer as
well as the ARM EHABI printer. This allows for a reasonably thorough look into
the encoded data.