[AArch64][ELF][PAC] Enable arm64e-like options via -mbranch-protection=pauthabi

[kovdan01]

• Enable all default arm64e pauth features
• Enable the following additional pauth features:
  • function pointers signing in init/fini arrays
  • vtable pointer address and type discrimination

Initially implemented in ff95e04d4d498827404e7fc30c27ea22a074871c, the init/fini stuff implemented later in 4fb933cc2d3629905a7ddf56ae96276484371a3d.