Fix unreachable code warnings when all reconnectable swift routes have compat wrappers

[julianlocke]

Background compatible routes get generated reconnection wrapper types. If they're in the allow list for Objective-C compatibility generation as well, an additional Objective-C wrapper type will be generated. If we generate an Objective C compatibility wrapper for each Swift one, a switch statement used to map from one to the other will contain an unreachable default statement. Since each layer is generated in separate (and potentially parallel) code generation passes, it's difficult make the generation logic smart enough to know whether to include the default. This change eliminates the warning by generating a different control flow that accommodates both situations naturally.

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##             fix-route-name-collisions     #347   +/-   ##
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