CRE: add "CJK width scaling" option

The setting is handled like all other bottom menu options
but, as it's really not useful and its target audience is
very limited, make it not shown in the bottom menu, but
available via another button in the (also quite not useful)
Word Expansion fine tuning widget.

frontend/apps/reader/modules/readerfont.lua

@@ -145,6 +145,11 @@ function ReaderFont:onReadSettings(config)
                        or 0
     self.ui.document:setWordExpansion(self.word_expansion)
 
+    self.cjk_width_scaling = config:readSetting("cjk_width_scaling")
+                       or G_reader_settings:readSetting("copt_cjk_width_scaling")
+                       or 100
+    self.ui.document:setCJKWidthScaling(self.cjk_width_scaling)
+
     self.line_space_percent = config:readSetting("line_space_percent")
                            or G_reader_settings:readSetting("copt_line_spacing")
                            or DCREREADER_CONFIG_LINE_SPACE_PERCENT_MEDIUM
@@ -261,6 +266,14 @@ function ReaderFont:onSetWordExpansion(value)
     return true
 end
 
+function ReaderFont:onSetCJKWidthScaling(value)
+    self.cjk_width_scaling = value
+    self.ui.document:setCJKWidthScaling(value)
+    self.ui:handleEvent(Event:new("UpdatePos"))
+    Notification:notify(T(_("CJK width scaling set to: %1%."), value))
+    return true
+end
+
 function ReaderFont:onSetFontGamma(gamma)
     self.gamma_index = gamma
     self.ui.document:setGammaIndex(self.gamma_index)
@@ -279,6 +292,7 @@ function ReaderFont:onSaveSettings()
     self.ui.doc_settings:saveSetting("font_kerning", self.font_kerning)
     self.ui.doc_settings:saveSetting("word_spacing", self.word_spacing)
     self.ui.doc_settings:saveSetting("word_expansion", self.word_expansion)
+    self.ui.doc_settings:saveSetting("cjk_width_scaling", self.cjk_width_scaling)
     self.ui.doc_settings:saveSetting("line_space_percent", self.line_space_percent)
     self.ui.doc_settings:saveSetting("gamma_index", self.gamma_index)
 end