[AArch64] Make +pauth enabled in Armv8.3-a by default (#78027)

Add AEK_PAUTH to ARMV8_3A in TargetParser and let it propagate to
ARMV8R, as it aligns with GCC defaults.

After adding AEK_PAUTH, several tests from TargetParserTest.cpp crashed
when trying to format an error message, thus update a format string in
AssertSameExtensionFlags to account for bitmask being pre-formatted as
std::string.

The CHECK-PAUTH* lines in aarch64-target-features.c are updated to
account for the fact that FEAT_PAUTH support and pac-ret can be enabled
independently and all four combinations are possible.

(cherry picked from commit a52eea66)