Fix locations of shadowing warnings in ms_transform

A shadowed variable in an ms_transform match expression emits a warning
located at the match expression instead of the variable.
Use erl_parse:get_attribute/2 in cover

Avoids treating node attributes as a simple line number, to ensure that any
change to the attributes format won't break cover.
Merge branches 'erl_scan-file-attribute', 'erl_scan-fix-column-tracking', 'ms_transform-locate-shadow-warning' and 'cover-get_attribute' into compile-column-numbers
Teach erl_scan the range option

This new option makes erl_scan return the location ranges of each scanned token.