TextWidget: small refactoring, better handle max_width (#5503)

Lots of code was doing some renderText calls to get the size
of some text string, and truncate it to some width if needed,
with or without an added ellipsis, before instantiating
a TextWidget with that tweaked text string.

This PR fixes/adds some properties and methods to TextWidget
so all that can be done by it. It makes the calling code
simpler, as they don't need to use RenderText directly.
(Additionally, when we go at using Harfbuzz for text rendering,
we'll just have to update or replace textwidget.lua without
the need to update any higher level code.)

Also:
- RenderText: removed the space added by truncateTextByWidth
  after the ellipsis, as it doesn't feel needed, and break
  right alignment of the ellipsis with other texts.
- KeyValuePage: fix some subtle size and alignment issues.
- NumberPickerWidget: fix font size (provided font size was
  not used)

frontend/ui/rendertext.lua

@@ -263,8 +263,7 @@ function RenderText:renderUtf8Text(dest_bb, x, baseline, face, text, kerning, bo
     return pen_x
 end
 
-local ellipsis, space = "…", " "
-local ellipsis_width, space_width
+local ellipsis = "…"
 --- Returns a substring of a given text that meets the maximum width (in pixels)
 -- restriction with ellipses (…) at the end if required.
 --
@@ -273,23 +272,13 @@ local ellipsis_width, space_width
 -- @int width maximum width in pixels
 -- @bool[opt=false] kerning whether the text should be measured with kerning
 -- @bool[opt=false] bold whether the text should be measured as bold
--- @bool[opt=false] prepend_space whether a space should be prepended to the text
 -- @treturn string
 -- @see getSubTextByWidth
-function RenderText:truncateTextByWidth(text, face, max_width, kerning, bold, prepend_space)
-    if not ellipsis_width then
-        ellipsis_width = self:sizeUtf8Text(0, max_width, face, ellipsis).x
-    end
-    if not space_width then
-        space_width = self:sizeUtf8Text(0, max_width, face, space).x
-    end
-    local new_txt_width = max_width - ellipsis_width - space_width
+function RenderText:truncateTextByWidth(text, face, max_width, kerning, bold)
+    local ellipsis_width = self:sizeUtf8Text(0, max_width, face, ellipsis, false, bold).x
+    local new_txt_width = max_width - ellipsis_width
     local sub_txt = self:getSubTextByWidth(text, face, new_txt_width, kerning, bold)
-    if prepend_space then
-        return space.. sub_txt .. ellipsis
-    else
-        return sub_txt .. ellipsis .. space
-    end
+    return sub_txt .. ellipsis
 end
 
 return RenderText