[yaml2obj] - Add `ELFYAML::YAMLIntUInt` to fix how we parse a relocation `Addend` key.

This patch makes `Relocation::Addend` to be `ELFYAML::YAMLIntUInt` and not `int64_t`.

`ELFYAML::YAMLIntUInt` it is a new type and it has the following benefits/features:

1) For an 64-bit object any hex/decimal addends
   in the range [INT64_MIN, UINT64_MAX] is accepted.
2) For an 32-bit object any hex/decimal addends
   in range [INT32_MIN, UINT32_MAX] is accepted.
3) Negative hex numbers like -0xffffffff are not accepted.
4) It is printed as decimal. I.e. obj2yaml will print
   something like "Addend: 125", this matches the current behavior.

This fixes all FIXMEs in `relocation-addend.yaml`.

Differential revision: https://reviews.llvm.org/D75527