[Swift] Remove repeated epsilon transitions in ATN.
[Swift] Remove repeated epsilon transitions in ATN.

Port the cset 125a509e from the Java runtime.  This adds checks to ATNState
to remove any repeated edges.  This was PR #1369 for the Java runtime.

parrt/antlr4,antlr/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,parrt/antlr4,antlr/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,parrt/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4