[clang] [Clang][AArch64]Add QCVTN builtin to SVE2.1 (PR #75454)

[Dinar Temirbulatov via cfe-commits]

================
@@ -0,0 +1,78 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
----------------
dtemirbulatov wrote:

Hmm, I could only see aarch64_sve_sqcvtn_x2 tests here, can you add aarch64_sve_sqcvtn_x4 as well?

https://github.com/llvm/llvm-project/pull/75454