[DWARFYAML] Add support for emitting value forms of strx, addrx, etc.

This patch adds support for emitting value forms of DW_FORM_strx,
DW_FORM_addrx, DW_FORM_loclistx and DW_FORM_rnglistx.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D83749