Previously, we’d look up the signal name as passed to (for example)
`g_signal_lookup()`, and rely on the fact that signals are inserted
twice into `g_signal_key_bsa`; once in canonical form and once not.
In preparation for only inserting signals into `g_signal_key_bsa` once,
we now try looking up a signal with the given signal name and, if that
fails, try canonicalising the name and trying again.
This is a performance hit on lookups for non-canonical names, but
shouldn’t affect the performance of lookups for canonical names. If
people want performance, they should use canonical names.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Helps: #358
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