apacheGH-49449: [C++] Backport xsimd neon fix (apache#49450)

### Rationale for this change
Performance in hot code.
There is a bug in xsimd where the rshift/lshift for Neon are implemented with a scalar loop instead of the appropriate SIMD intrinsics. This code path is core to the `unpack` routine in Parquet reads.
xtensor-stack/xsimd#1266

### What changes are included in this PR?
A bug backport.

### Are these changes tested?
Yes.

### Are there any user-facing changes?
No.

* GitHub Issue: apache#49449

Authored-by: AntoinePrv <AntoinePrv@users.noreply.github.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>

Author: AntoinePrv

cpp/src/arrow/util/bpacking_simd_kernel_internal.h

@@ -148,6 +148,10 @@ constexpr bool IsSse2 = std::is_base_of_v<xsimd::sse2, Arch>;
 template <typename Arch>
 constexpr bool IsAvx2 = std::is_base_of_v<xsimd::avx2, Arch>;
 
+/// Whether we are compiling for the Neon or above in the arm64 family.
+template <typename Arch>
+constexpr bool IsNeon = std::is_base_of_v<xsimd::neon, Arch>;
+
 /// Wrapper around ``xsimd::bitwise_lshift`` with optimizations for non implemented sizes.
 //
 // We replace the variable left shift by a variable multiply with a power of two.
@@ -196,6 +200,15 @@ auto left_shift(const xsimd::batch<Int, Arch>& batch,
     return xsimd::bitwise_cast<Int>(shifted0 | shifted1);
   }
 
+  // TODO(xsimd) bug fixed likely in xsimd>14.0.0
+  // https://github.com/xtensor-stack/xsimd/pull/1266
+  if constexpr (IsNeon<Arch>) {
+    using SInt = std::make_signed_t<Int>;
+    constexpr auto signed_shifts =
+        xsimd::batch_constant<SInt, Arch, static_cast<SInt>(kShifts)...>();
+    return xsimd::kernel::bitwise_lshift(batch, signed_shifts.as_batch(), Arch{});
+  }
+
   return batch << shifts;
 }
 
@@ -252,6 +265,15 @@ auto right_shift_by_excess(const xsimd::batch<Int, Arch>& batch,
     return xsimd::bitwise_rshift<kMaxRShift>(left_shift(batch, kLShifts));
   }
 
+  // TODO(xsimd) bug fixed likely in xsimd>14.0.0
+  // https://github.com/xtensor-stack/xsimd/pull/1266
+  if constexpr (IsNeon<Arch>) {
+    using SInt = std::make_signed_t<Int>;
+    constexpr auto signed_shifts =
+        xsimd::batch_constant<SInt, Arch, static_cast<SInt>(kShifts)...>();
+    return xsimd::kernel::bitwise_rshift(batch, signed_shifts.as_batch(), Arch{});
+  }
+
   return batch >> shifts;
 }