Add custom measurement operations to Q#

[orpuente-MS]

This PR adds the ability to declare custom measurements in Q#. Here is an example:

@Measurement()
operation __quantum__qis__mx__body(target : Qubit) : Result {
  body intrinsic;
}

The generated QIR will be,

declare void @__quantum__qis__mx__body(%Qubit*, %Result*) #1

Design Notes

1. I choose the @Measurement() attribute over a new measurement keyword to avoid putting extra syntax into the language.
2. A custom measurement must be a body intrinsic or a @SimulatableIntrinsic().
3. A measurement must take only Qubits as inputs and have Results as outputs.

Notes to reviewers

This PR consists of the following steps:

1. Adding a @Measurement() attribute to the language and piping it down to FIR.
2. Make the generated QIR have the #1 attribute indicating an irreversible operation.
3. Treating a measurement as a dynamic operation in RCA.
4. Handling custom measurements correctly during partial evaluation: moving the output Results to result registers in the input.
5. Handling undesired semantics as errors using an HIR pass.
6. Adding the @Measurement() attribute to the completions list.
7. Unit tests in codegen and in the HIR pass.

Next steps

After this PR is merged we can add the @Measurement() attribute to the measurement operations in the standard library and remove the hard coded logic we have for them in the compiler.

[minestarks]

Heads up, this code is changing in my PR. When you hit the merge conflict, I suggest just reverting this and searching again for the attribute list instead of trying to resolve it as a merge conflict...

[minestarks]

@orpuente-MS Do we really need an explicit @Measurement attribute if we simply define a "measurement intrinsic" as an "intrinsic that returns a Result"?