Fractional UI scaling support

[DuMOHsmol]

At the moment, SDR++ allows only integer UI scaling options: 100%, 200%, etc. But for some displays, 100% is too small and 200% is too huge. It would be nice to gain some level of fractional scaling support.

[DuMOHsmol]

Currently, the fractional scaling options can't be added right away because some widgets become misaligned (see discussion in https://github.com/AlexandreRouma/SDRPlusPlus/pull/1115).

[DuMOHsmol]

@AlexandreRouma, how do you think about allowing arbitrary uiScale fractions in config file without exposing new options in UI until everything is fixed?

For me it's currently the choice between something being misaligned and the whole app being at inconvenient scale, and I would rather pick the first option. Fun fact: I have actually used a private fork of SDR++ with all fonts scaled up before there was any scaling support. Everything was misaligned, but it still was better than squinting at everything.

[bczhc]

I have a 23.8'', 2560x1440 display, and 150% will be just fine. I had forked sdrpp and modified it, adding my 150% option:

diff --git a/core/src/gui/menus/display.cpp b/core/src/gui/menus/display.cpp
index 59649ed..a9f2422 100644
--- a/core/src/gui/menus/display.cpp
+++ b/core/src/gui/menus/display.cpp
@@ -122,6 +122,7 @@ namespace displaymenu {
         // Define and load UI scales
         uiScales.define(1.0f, "100%", 1.0f);
         uiScales.define(2.0f, "200%", 2.0f);
+        uiScales.define(1.5f, "150%", 1.5f);
         uiScales.define(3.0f, "300%", 3.0f);
         uiScales.define(4.0f, "400%", 4.0f);
         uiScaleId = uiScales.valueId(style::uiScale);

and, used it for a long time, everything is fine. No font and widget issues etc, at least as yet.

Also btw, I just updated SDR++, and it crashes on launch. After a debug, the cause is: uiScaleId = uiScales.valueId(style::uiScale);. SDR++ cannot find a menu option corresponding to the 1.5 scaling factor defined in the config file. I think at least, we should allow users to use custom scaling factors by modifying the config file.