Users might want to assign custom tracknames, which requires deleting the
default name either entirely or parts of it.
By pre-selecting parts of the trackname, users can start typing right away
after opening the dialog. `Ctrl+A` to select everything is still possible,
but keeping the distance in the filename by default comes in handy,
e.g. when using a file manager not displaying the track length.
NB: Might need adaptation once trackname validation becomes less strict,
i.e. currently "(" and "->" as specified in the message catalog are replaced
with ' - ' by the validator before being inserted into the dialog.
Test Plan:
- Open "Export" dialog ("Location - Other Location - 2km")
- Open "Export" dialog for roundtrip ("Location - 1km")
- In both cases the complete trackname except for the distance
information (including separator) should be selected.
- No unwanted behaviour even if Nominatim is slow or down.
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