Printing: fix text resolution

Scintilla doesn't respect the context resolution, so we need to scale
its draws ourselves.
Printing: draw the vertical separator line more accurately

Use the dimensions and offsets used by Scintilla to position our
separator line, since its position depends on where Scintilla drawn.

Closes #3580268.
Printing: fix improper margins when printing to a physical device

We were improperly adding the printing device margins to the area
where we print, leading to wider margins on physical outputs than
on PDF or preview outputs (which have no hard margins), as well as
wasting space and not respecting user's settings.

Closes #3580269.
Scintilla: properly update the Pango contexts for the target surface

This fixes drawing on a surface that has different settings (like
scaling) than the display surface, by performing the measurements on a
layout properly set up for the target surface.

In practice, this fixes e.g. printing on a scaled surface.

(Applied to Scintilla HG as 74c71632dd1afa726b0f1608d13413e0864da9b0)
Merge branch 'printing-with-scintilla'
Revert "Alter default and document icon setting"

This reverts commit 306eaab3916649567c892215ad8390b9d39de82f.
Revert "Make use of theme icon a various pref."

A preference for an icon doesn't make sense;  if someone don't like
her theme's icon she should either switch to another theme, override
that specific icon or don't bother.

This reverts commit 6897cd49c69535c6563e56ae011c6f8382fec485.
Use the Geany icon from the theme everywhere
Replace images embedded in the sources with proper themable icons

Additionally, provide SVG versions of the icons as well as them
rendered at the various icons sizes.
Use icons from the theme in the completion popup

Drop the XPM icons and load the PNG ones through the theme mechanisms,
like we do for the symbols tree.
Optimize PNG icons
Merge branch 'use-named-icons'