[RFC] Library-mode and kernel_builder implementation of allocation with initialization

[amccaskey]

Initial prototype of #1086 for library mode and the kernel_builder

Things that still need to be done:

• Python bindings
• Testing
• Update simulators to set state data (custatevec, cutensornet, mgpu)
• Hook up the ASTBridge
• Review / refactor InitializeStateOp and LowerToQIR.cpp updates (@schweitzpgi)
• Verify bit ordering (@boschmitt)

Here's the "test" I've been running (will update to add some tests)

#include "cudaq.h"
#include <iostream> 

__qpu__ auto test0() {
  cudaq::qubit q = {0., 1.};
  return mz(q);
}

__qpu__ auto test1() {
  cudaq::qubit q = cudaq::ket::one;
  return mz(q);
}

__qpu__ void test2() { cudaq::qubit q = {M_SQRT1_2, M_SQRT1_2}; }

__qpu__ void test3() { cudaq::qvector q = {M_SQRT1_2, 0., 0., M_SQRT1_2}; }

__qpu__ void test4(const std::vector<cudaq::complex> &state) {
  cudaq::qvector q = state;
}

int main() {
  for (auto i : cudaq::range(10))
    printf("Test 0: %d\n", static_cast<int>(test0()));
  for (auto i : cudaq::range(10))
    printf("Test 1: %d\n", static_cast<int>(test1()));
  cudaq::sample(test2).dump();
  cudaq::sample(test3).dump();

  std::vector<cudaq::complex> vec{M_SQRT1_2, 0., 0., M_SQRT1_2};
  cudaq::sample(test4, vec).dump();

  // test error scenarios
  //
  // bad number of elements, this throws
  //     cudaq::sample(test4, std::vector<cudaq::complex>{1., 2., 3.});
  // vector not normalized, this throws
  //   cudaq::sample(test4, std::vector<cudaq::complex>{1., 2., 3., 4.});

  // Test kernel builder
  auto kernel = cudaq::make_kernel();
  auto qubits = kernel.qalloc(vec);
  std::cout << kernel << "\n";
  cudaq::sample(kernel).dump();
  return 0;
}

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