[DebugInfo][BPF] Add 'annotations' field for DIBasicType & DISubroutineType (#91422)

Extend `DIBasicType` and `DISubroutineType` with additional field
`annotations`, e.g. as below:

```
  !5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed, annotations: !6)
  !6 = !{!7}
  !7 = !{!"btf:type_tag", !"tag1"}
```

The field would be used by BPF backend to generate DWARF attributes
corresponding to `btf_type_tag` type attributes, e.g.:

```
  0x00000029:   DW_TAG_base_type
                  DW_AT_name	("int")
                  DW_AT_encoding	(DW_ATE_signed)
                  DW_AT_byte_size	(0x04)

  0x0000002d:     DW_TAG_LLVM_annotation
                    DW_AT_name	("btf:type_tag")
                    DW_AT_const_value	("tag1")
```

Such DWARF entries would be used to generate BTF definitions by tools
like [pahole](https://github.com/acmel/dwarves).

Note: similar fields with similar purposes are already present in
DIDerivedType and DICompositeType.

Currently "btf_type_tag" attributes are represented in debug information
as 'annotations' fields in DIDerivedType with DW_TAG_pointer_type tag.
The annotation on a pointer corresponds to pointee having the attributes
in the final BTF.

The discussion in
[thread](https://lore.kernel.org/bpf/87r0w9jjoq.fsf@oracle.com/) came to
conclusion, that such annotations should apply to the annotated type
itself. Hence the necessity to extend `DIBasicType` & `DISubroutineType`
types with 'annotations' field to represent cases like below:

```
  int __attribute__((btf_type_tag("foo"))) bar;
```

This was previously tracked as differential revision:
https://reviews.llvm.org/D143966