Tame some ButtonTable users into re-using Buttontable instances if possible (#7166)

* QuickDictLookup, ImageViewer, NumberPicker: Smarter `update` that will re-use most of the widget's layout instead of re-instantiating all the things.
* SpinWidget/DoubleSpinWidget: The NumberPicker change above renders a hack to preserve alpha on these widgets almost unnecessary. Also fixed said hack to also apply to the center, value button.

* Button: Don't re-instantiate the frame in setText/setIcon when unnecessary (e.g., no change at all, or no layout change).
* Button: Add a refresh method that repaints and refreshes a *specific* Button (provided it's been painted once) all on its lonesome.

* ConfigDialog: Free everything that's going to be re-instatiated on update
 
* A few more post #7118 fixes:
  * SkimTo: Always flag the chapter nav buttons as vsync
  * Button: Fix the highlight on rounded buttons when vsync is enabled (e.g., it's now entirely visible, instead of showing a weird inverted corner glitch).
  * Some more heuristic tweaks in Menu/TouchMenu/Button/IconButton
* ButtonTable: fix the annoying rounding issue I'd noticed in #7054 ;).

* Enable dithering in TextBoxWidget (e.g., in the Wikipedia full view). This involved moving the HW dithering align fixup to base, where it always ought to have been ;).

* Switch a few widgets that were using "partial" on close to "ui", or, more rarely, "flashui". The intent being to limit "partial" purely to the Reader, because it has a latency cost when mixed with other refreshes, which happens often enough in UI ;).

* Minor documentation tweaks around UIManager's `setDirty` to reflect that change.

* ReaderFooter: Force a footer repaint on resume if it is visible (otherwise, just update it).
* ReaderBookmark: In the same vein, don't repaint an invisible footer on bookmark count changes.

frontend/ui/widget/numberpickerwidget.lua

@@ -62,10 +62,8 @@ function NumberPickerWidget:init()
         self.value_index = self.value_index or 1
         self.value = self.value_table[self.value_index]
     end
-    self:update()
-end
 
-function NumberPickerWidget:paintWidget()
+    -- Widget layout
     local bordersize = Size.border.default
     local margin = Size.margin.default
     local button_up = Button:new{
@@ -118,18 +116,19 @@ function NumberPickerWidget:paintWidget()
     local empty_space = VerticalSpan:new{
         width = math.ceil(self.screen_height * 0.01)
     }
-    local value = self.value
+
+    self.formatted_value = self.value
     if not self.value_table then
-        value = string.format(self.precision, value)
+        self.formatted_value = string.format(self.precision, self.formatted_value)
     end
 
     local input_dialog
     local callback_input = nil
     if self.value_table == nil then
-        callback_input =  function()
+        callback_input = function()
             input_dialog = InputDialog:new{
                 title = _("Enter number"),
-                input = value,
+                input = self.formatted_value,
                 input_type = "number",
                 buttons = {
                     {
@@ -170,36 +169,33 @@ function NumberPickerWidget:paintWidget()
                     },
                 },
             }
+            self.update_callback()
             UIManager:show(input_dialog)
             input_dialog:onShowKeyboard()
         end
     end
 
-    local text_value = Button:new{
-        text = tostring(value),
+    self.text_value = Button:new{
+        text = tostring(self.formatted_value),
         bordersize = 0,
         padding = 0,
         text_font_face = self.spinner_face.font,
         text_font_size = self.spinner_face.orig_size,
         width = self.width,
         max_width = self.width,
+        show_parent = self.show_parent,
         callback = callback_input,
     }
-    return VerticalGroup:new{
+
+    local widget_spinner = VerticalGroup:new{
         align = "center",
         button_up,
         empty_space,
-        text_value,
+        self.text_value,
         empty_space,
         button_down,
     }
-end
 
---[[--
-Update.
---]]
-function NumberPickerWidget:update()
-    local widget_spinner = self:paintWidget()
     self.frame = FrameContainer:new{
         bordersize = 0,
         padding = Size.padding.default,
@@ -217,6 +213,22 @@ function NumberPickerWidget:update()
     UIManager:setDirty(self.show_parent, function()
         return "ui", self.dimen
     end)
+end
+
+--[[--
+Update.
+--]]
+function NumberPickerWidget:update()
+    self.formatted_value = self.value
+    if not self.value_table then
+        self.formatted_value = string.format(self.precision, self.formatted_value)
+    end
+
+    self.text_value:setText(tostring(self.formatted_value), self.width)
+
+    UIManager:setDirty(self.show_parent, function()
+        return "ui", self.dimen
+    end)
     self.update_callback()
 end