Replace some Fixed types with Threshold in index.theme files

[SmartFinn]

This PR allows:

• scaling actions icons 16px to 32px, 22px to 44px, 24px to 48px
• scaling 32x32/emblems to 64px/96px/128px/160px/192px/224px/256px
• scaling 48x48/* to 96px/144px
• scaling 64x64/* to 128px/192px/256px

It fixes the previous behavior that blurring icons because:

• scaling 24x24/actions icons to 32px/44px
• scaling 48x48/emblems to 64px/128px/192px/256px
• scaling 64x64/* to 96px/144px

The changes tested in GNOME and should be tested in other DE before merging.

Details https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html

[varlesh]

Tested on KDE & Pantheon. I'm not seen bugs)

[SmartFinn]

Unfortunately Type=Threshold doesn't work as I expected. It doesn't allow scaling 22px to 44px, it allows scaling 48px to 96px, but Type=Fixed do the same. To correct support 44px and other scaling resolutions need to add workaround as I added for 96px. Only the following snippets are incorrect and should be deleted:

[64x64/*]
Context=*
Size=64
Scale=2
MinSize=64
MaxSize=512
Type=Scalable

[SmartFinn]

Scaling to 96px works fine in GTK-based, but not in Plasma Desktop. Neither Type=Fixed nor Type=Threshold. To add the icon resolution in KDE need to add the workaround back. It will be implemented in the very next release.