Work on extending QASM to support extern quantum subroutines

OPENQASM 3;

const n_counting = 3;

// Declare external quantum subroutine:

def QCOR__IQFT__Interop qubit[n_counting]:qq extern;

// For this example, the oracle is the T gate 

// on the provided qubit

gate oracle b {

    t b;

}

// Define some counting qubits

qubit counting[n_counting];

// Allocate the qubit we'll 

// put the initial state on

qubit state;

// We want T |1> = exp(2*i*pi*phase) |1> = exp(i*pi/4)

// compute phase, should be 1 / 8;

// Initialize to |1>

x state;

// Put all others in a uniform superposition

h counting;

// Loop over and create ctrl-U**2k

int repetitions = 1;

for i in [0:n_counting] {

    ctrl @ pow(repetitions) @ oracle counting[i], state;

    repetitions *= 2;

}

// Run inverse QFT 

QCOR__IQFT__Interop counting;

// Now lets measure the counting qubits

bit c[n_counting];

measure counting -> c;

// Backend is QPP which is lsb, 

// so return should be 100

print(c);

EQUALS=106

ARROW=107

MINUS=108

Constant=109

Whitespace=110

Newline=111

Integer=112

Identifier=113

RealNumber=114

TimingLiteral=115

StringLiteral=116

LineComment=117

BlockComment=118

EXTERN=109

Constant=110

Whitespace=111

Newline=112

Integer=113

Identifier=114

RealNumber=115

TimingLiteral=116

StringLiteral=117

LineComment=118

BlockComment=119

'OPENQASM'=1

'include'=2

'QCOR_EXPECT_TRUE'=3

'='=106

'->'=107

'-'=108

'extern'=109

    T__86 = 87, T__87 = 88, T__88 = 89, T__89 = 90, T__90 = 91, T__91 = 92, 

    T__92 = 93, T__93 = 94, T__94 = 95, LBRACKET = 96, RBRACKET = 97, LBRACE = 98, 

    RBRACE = 99, LPAREN = 100, RPAREN = 101, COLON = 102, SEMICOLON = 103, 

    DOT = 104, COMMA = 105, EQUALS = 106, ARROW = 107, MINUS = 108, Constant = 109, 

    Whitespace = 110, Newline = 111, Integer = 112, Identifier = 113, RealNumber = 114, 

    TimingLiteral = 115, StringLiteral = 116, LineComment = 117, BlockComment = 118

    DOT = 104, COMMA = 105, EQUALS = 106, ARROW = 107, MINUS = 108, EXTERN = 109, 

    Constant = 110, Whitespace = 111, Newline = 112, Integer = 113, Identifier = 114, 

    RealNumber = 115, TimingLiteral = 116, StringLiteral = 117, LineComment = 118, 

    BlockComment = 119

  };

  explicit qasm3Lexer(antlr4::CharStream *input);