[torch.fx] Fix pattern matching single node multiple times

[thomasw21]

Related to pytorch#66442

def f(x):
    y = torch.sigmoid(x)
    z = torch.sigmoid(x)
    return y + z

def pattern(x):
    return torch.sigmoid(x)

def replacement(x):
    return torch.relu(x)

def comparison(x):
    y = torch.relu(x)
    z = torch.relu(x)
    return y + z

traced = symbolic_trace(f)

subgraph_rewriter.replace_pattern(traced, pattern, replacement) # This replaces only one sigmoid

As shown in the code previously, we allow a single node to match a pattern multiple time. This is need if you look at the traced f:

# Tracing f
.graph():
    %x : [#users=2] = placeholder[target=x]
    %sigmoid : [#users=1] = call_function[target=torch.sigmoid](args = (%x,), kwargs = {})
    %sigmoid_1 : [#users=1] = call_function[target=torch.sigmoid](args = (%x,), kwargs = {})
    %add : [#users=1] = call_function[target=operator.add](args = (%sigmoid, %sigmoid_1), kwargs = {})
    return add

You can see that add aggregates two values.

This is mainly due to the matching algorithm to support on Dict[Node, Node] where the key are pattern nodes and values are nodes living in the graph module graph.

[thomasw21]

Closing in favor of #2