[DWARFDump] Make --verify handle all sections by default (#81559)

The current behavior of --verify is that it only verifies debug_info,
debug_abbrev and debug_names. This seems fairly arbitrary and might have
been unintentional, as originally the absence of any section flags
implied "all".

This patch changes the behavior so that the verifier now verifies
everything by default. It revealed two tests that had potentially
invalid DWARF:

1. dwarfdump-str-offsets.s is adding padding between two
debug_str_offset contributions. The standard does not explicitly allow
this behavior. See issue
https://github.com/llvm/llvm-project/issues/81558

2. dwarf5-macro.test uses a checked-in binary that has invalid
debug_str_offsets. One of its entries points to the _middle_ of the
string section:

error: .debug_str_offsets: contribution 0x0: index 0x4: invalid string
offset *0x18 == 0x455D, is neither zero nor immediately following a null
character

If we look at the closest offset to 0x455D in debug_str:

```
0x0000454e: "__SLONG32_TYPE int"
```

0x455D points to "int".