Classical types indexing in OpenQASM

[orpuente-MS]

This PR adds classical type indexing support to our OpenQASM compiler and fixes two bugs.

Highlights

The major challenge of this PR was supporting classical type indexing in the left-hand side of assignment expressions. The idea to make it work is compiling

int[4] a = 0b1111;
a[1:][1:] = "01";

to this

mutable a = 15;
a = {
    mutable bitarray = Std.OpenQASM.Convert.IntAsResultArrayBE(a, 4);
    bitarray[1...][1...] = [Zero, One];
    Std.OpenQASM.Convert.ResultArrayAsIntBE(bitarray)
};

so that we can leverage Q#'s array semantics.
 
The indexing infrastructure is now simpler. Instead of having different codepaths for indexed identifiers and indexed expressions, now we just have a codepath for indexed expressions. (The codepath for indexed identifiers was redundant).

Multiple indexing is now expressed as nested IndexedExpr structs with a single index each, instead of a single IndexedExpr with a list of indices. This makes thinking about indexing simpler, since now the utility functions to handle indexing just need to handle a single index. It also makes compilation simpler, since this is how the Q# AST is structured.

Bug fixes:

1. Consecutive slices into an array now act on the same dimension, instead of acting on consecutive dimensions.
2. AngleAsResultArrayBE is now correctly exported in the Angle.qs file instead of AngleAsResultArray.

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 11dfc2b

Test	This Branch	On Main	Difference
compile core + standard lib	25669290 bytes	25677846 bytes	-8556 bytes

[idavis]

In what case can the bitarray take multiple indices?

[orpuente-MS]

You can apply multiple consecutive slices to a bitarray

const bit[4] a = "1010";
a[1:][1:]

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 966a8c5

Test	This Branch	On Main	Difference
compile core + standard lib	25669290 bytes	25677846 bytes	-8556 bytes

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 4b97c11

Test	This Branch	On Main	Difference
compile core + standard lib	25669290 bytes	25677846 bytes	-8556 bytes