[Finii]

[why]
Except when a Nerd Font Mono font is created, i.e. for all non-mono fonts: The centered icons are centered within 1 cell space. If that is not big enough the icon is left-aligned (filling the left cell completely and a varying amount of the left part of the right cell).

Having vertical colums of these icons might look strange because a center alignment seems more natural in some situations.

[how]
A new experimental command line switch is added that switches the scaling for 'pa' stretch to stretch into 2 cells.

For the Powerline glyphs E0Ax the rules are changed to explicitely require scaling into 1 cell to prevent application of the new rule here.

To use this add --experimental center-wide to the font-patcher command line.

Fixes: #1330
Fixes: #2012

Requirements / Checklist

• Read the Contributing Guidelines
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan.
  Issue number where discussion took place: #xxx
• If this contains a font/glyph add its origin as background info below (e.g. URL)
• Verified the license of any newly added font, glyph, or glyph set. License is: xxx

What does this Pull Request (PR) do?

How should this be manually tested?

Any background context you can provide?

The implementation follows @rivy closely and takes @powerman's finding about E0Ax into account.

What are the relevant tickets (if any)?

Screenshots (if appropriate or helpful)

The re-centered glyphs have a dark blue mark:

Pomicons shifted slightly to the right, most Powerline glyphs stay where they are

_Icons shifted to the right, so that they are center aligned on border of cell1 and cell2_