This patch adds more flexibility to the original VFABI demangling API.
- Allow demangling an empty parameter list, which is explicitly allowed by X86 VFABI doc (section 2.6) and probably implicitly allowed by AArch64 VFABI doc (section 4.1) as well.
- Allow passing the module as a nullptr, so that we don't check the existence of the demangled vector function name. This is useful when we want to create the widened function according to the demangling result.
Signed-off-by: Yilong Guo <email@example.com>