Linemap force location and remove LINEMAP_POSITION_FOR_COLUMN (issue4801090)

[Gabriel Charette]

> I also removed LINEMAP_POSITION_FOR_COLUMN, it did the EXACT same thing as linemap_position_for_column, so maintaining both in parallel seems like overkill to me. The only thing I can think of is that it's more optimal as it's inlined (but if that's really needed we can always make linemap_position_for_column an inline function).
>

This section of the patch is somewhat independent and has not been
discussed in this thread, I pulled it out and submitted a separate
patch (issue4874043) while I'm working on making this patch force
location from cpp_reader.

Gabriel