fix(select): assign result of track exp to element value

Fixes a regression where the option/select values would always be set to
the key or index of a value within the corresponding collection. Prior to
some 1.3.0 refactoring, the result of the track expression would be bound
to the value, but this behavior was not documented or explicitly tested.

This commit adds one explicit test for this behavior, and changes 
several other trackBy tests to reflect the desired behavior as well.

Fixes #9592