[DWARFYAML] Implement the .debug_loclists section.

This patch implements the .debug_loclists section. There are only two
DWARF expressions are implemented in this patch (DW_OP_consts,
DW_OP_stack_value). We will implement more in the future.

The YAML description of the .debug_loclists section is:

```
debug_loclists:
  - Format:              DWARF32 ## Optional
    Length:              0x1234  ## Optional
    Version:             5       ## Optional (5 by default)
    AddressSize:         8       ## Optional
    SegmentSelectorSize: 0       ## Optional (0 by default)
    OffsetEntryCount:    1       ## Optional
    Offsets:             [ 1 ]   ## Optional
    Lists:
      - Entries:
          - Operator:          DW_LLE_startx_endx
            Values:            [ 0x1234, 0x4321 ]
            DescriptorsLength: 0x1234             ## Optional
            Descriptors:
              - Operator: DW_OP_consts
                Values:   [ 0x1234 ]
```

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D84234