This patch introduces MCInstPrinter::setMarkupSpans, which allows the caller to
use the output of rich disassembly without parsing its output string.
An upcoming patch replaces markup() with startMarkup() and endMarkup().
This feature will be used for the highlighting feature in llvm-objdump.
[X86] X86ATTInstPrinter: replace markup with startMarkup/endMarkup
[llvm-objcopy] Implement highlighting
As the first step, this patch highlights some elements: registers and immediate values,
and some symbol names.