Improvement: Make "tap" function available in reader mode

[3e4]

Tap function shows list of layers for polygons below pointer. This function is only available in klayout -e. (0.27.3)

Function should be also available in reader mode as it does not alter the layout and is a useful investigation function.

[klayoutmatthias]

Hi @3e4,

I employed the DeLorean time machine approach from "Back to the future" (https://www.popularmechanics.com/culture/movies/a17862/back-to-the-future-time-machines-schematics/) to implement the solution before this ticket was issued: 98e20cf

I'm only able to cover 8 hours as of now, but I'm working on a larger time leap within this retrograde bug fix approach - specifically before the previous release.

Matthias

[klayoutmatthias]

Released with 0.27.4