[llvm-readobj][COFF] Consistent PDBGUID Formatting (#94256)

## Consistent PDB GUID in `llvm-readobj`

Currently, the PDB GUID is shown as a byte array:
`PDBGUID: (D8 4C 88 D9 26 15 1F 11 4C 4C 44 20 50 44 42 2E)`

This is inconsistent with `llvm-pdbutil` (e.g. `llvm-pdbutil dump
--summary`) which shows it as a hexadecimal string.
Additionally, `yaml2obj` uses the same hexadecimal string format.

In general, the hexadecimal string is the common representation for PDB
GUIDs on Windows.

This PR changes it to be consistent as shown below:
`PDBGUID: {D9884CD8-1526-111F-4C4C-44205044422E}`