Add sugar types for pack-indexed builtins

[ilya-biryukov]

#106730 added the __builtin_dedup_pack, but it lacks some sugar after substitution, see the FIXME

llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp

Line 1730 in db63c57

// FIXME: add ability to represent sugarred type for N-th element of a

We need to be careful to make the resulting operations linear and avoid quadratic compile times as in #153431.
Otherwise sharing the common data and concepts with PackIndexingType should be beneficial for this, see

llvm-project/clang/include/clang/AST/Type.h

Line 6280 in db63c57

class PackIndexingType final

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Ilya Biryukov (ilya-biryukov)

#106730 added the `__builtin_dedup_pack`, but it lacks some sugar after substitution, see the FIXME https://github.com/llvm/llvm-project/blob/db63c57c59e67c65f487b2d88cbc9ac89dfdd01b/clang/lib/Sema/SemaTemplateInstantiate.cpp#L1730

We need to be careful to make the resulting operations linear and avoid quadratic compile times as in #153431.
Otherwise sharing the common data and concepts with PackIndexingType should be beneficial for this, see

llvm-project/clang/include/clang/AST/Type.h

Line 6280 in db63c57

class PackIndexingType final