[DWARFYAML] Add support for referencing different abbrev tables.

This patch adds support for referencing different abbrev tables. We use
'ID' to distinguish abbrev tables and use 'AbbrevTableID' to explicitly
assign an abbrev table to compilation units.

The syntax is:
```
debug_abbrev:
  - ID: 0
    Table:
      ...
  - ID: 1
    Table:
      ...
debug_info:
  - ...
    AbbrevTableID: 1 ## Reference the second abbrev table.
  - ...
    AbbrevTableID: 0 ## Reference the first abbrev table.
```

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D83116