Adding box pragma support to QASM compiler

[idavis]

Adding support for boxed expressions and pragmas for them when integrating with the Q# compiler.

When working in OpenQASM with the QDK, we can now use pragmas to denote parameterless void functions to call at the beginning and/or end of boxed expressions. They can additionally leverage simulatable intrinsic functions which will flow through to code generation.

OPENQASM 3.0;
include "stdgates.inc";
#pragma qdk.box.open box_begin
#pragma qdk.box.close box_end

@SimulatableIntrinsic
def box_begin() {}

@SimulatableIntrinsic
def box_end() {}

qubit q;
box {
    x q;
}
output bit c;
c = measure q;

define void @ENTRYPOINT__main() #0 {
block_0:
  call void @box_begin()
  call void @__quantum__qis__x__body(%Qubit* inttoptr (i64 0 to %Qubit*))
  call void @box_end()
  call void @__quantum__qis__m__body(%Qubit* inttoptr (i64 0 to %Qubit*), %Result* inttoptr (i64 0 to %Result*))
  call void @__quantum__rt__tuple_record_output(i64 0, i8* null)
  ret void
}

[swernli]

Looks good with a few minor comments. On the naming front, assuming we either ignore the syntax highlighting quirk or fix it, I think keeping the naming used in here (qdk.box.open) is good.