Clarify our OOP semantics across the codebase (#9586)

Basically:

* Use `extend` for class definitions
* Use `new` for object instantiations

That includes some minor code cleanups along the way:

* Updated `Widget`'s docs to make the semantics clearer.
* Removed `should_restrict_JIT` (it's been dead code since https://github.com/koreader/android-luajit-launcher/pull/283)
* Minor refactoring of LuaSettings/LuaData/LuaDefaults/DocSettings to behave (mostly, they are instantiated via `open` instead of `new`) like everything else and handle inheritance properly (i.e., DocSettings is now a proper LuaSettings subclass).
* Default to `WidgetContainer` instead of `InputContainer` for stuff that doesn't actually setup key/gesture events.
* Ditto for explicit `*Listener` only classes, make sure they're based on `EventListener` instead of something uselessly fancier.
* Unless absolutely necessary, do not store references in class objects, ever; only values. Instead, always store references in instances, to avoid both sneaky inheritance issues, and sneaky GC pinning of stale references.
  * ReaderUI: Fix one such issue with its `active_widgets` array, with critical implications, as it essentially pinned *all* of ReaderUI's modules, including their reference to the `Document` instance (i.e., that was a big-ass leak).
* Terminal: Make sure the shell is killed on plugin teardown.
* InputText: Fix Home/End/Del physical keys to behave sensibly.
* InputContainer/WidgetContainer: If necessary, compute self.dimen at paintTo time (previously, only InputContainers did, which might have had something to do with random widgets unconcerned about input using it as a baseclass instead of WidgetContainer...).
* OverlapGroup: Compute self.dimen at *init* time, because for some reason it needs to do that, but do it directly in OverlapGroup instead of going through a weird WidgetContainer method that it was the sole user of.
* ReaderCropping: Under no circumstances should a Document instance member (here, self.bbox) risk being `nil`ed!
* Kobo: Minor code cleanups.

frontend/apps/reader/modules/readerview.lua

@@ -28,28 +28,13 @@ local T = require("ffi/util").template
 
 local ReaderView = OverlapGroup:extend{
     document = nil,
+    view_modules = nil, -- array
 
     -- single page state
-    state = {
-        page = nil,
-        pos = 0,
-        zoom = 1.0,
-        rotation = 0,
-        gamma = 1.0,
-        offset = nil,
-        bbox = nil,
-    },
+    state = nil, -- table
     outer_page_color = Blitbuffer.gray(G_defaults:readSetting("DOUTER_PAGE_COLOR") / 15),
     -- highlight with "lighten" or "underscore" or "strikeout" or "invert"
-    highlight = {
-        lighten_factor = G_reader_settings:readSetting("highlight_lighten_factor", 0.2),
-        note_mark = G_reader_settings:readSetting("highlight_note_marker"),
-        temp_drawer = "invert",
-        temp = {},
-        saved_drawer = "lighten",
-        saved = {},
-        indicator = nil, -- geom: non-touch highlight position indicator: {x = 50, y=50}
-    },
+    highlight = nil, -- table
     highlight_visible = true,
     note_mark_line_w = 3, -- side line thickness
     note_mark_sign = nil,
@@ -58,12 +43,9 @@ local ReaderView = OverlapGroup:extend{
     -- PDF/DjVu continuous paging
     page_scroll = nil,
     page_bgcolor = Blitbuffer.gray(G_defaults:readSetting("DBACKGROUND_COLOR") / 15),
-    page_states = {},
+    page_states = nil, -- table
     -- properties of the gap drawn between each page in scroll mode:
-    page_gap = {
-        -- color (0 = white, 8 = gray, 15 = black)
-        color = Blitbuffer.gray((G_reader_settings:readSetting("page_gap_color") or 8) / 15),
-    },
+    page_gap = nil, -- table
     -- DjVu page rendering mode (used in djvu.c:drawPage())
     render_mode = G_defaults:readSetting("DRENDER_MODE"), -- default to COLOR
     -- Crengine view mode
@@ -91,10 +73,30 @@ local ReaderView = OverlapGroup:extend{
 
 function ReaderView:init()
     self.view_modules = {}
-    -- fix recalculate from close document pageno
-    self.state.page = nil
 
-    -- Reset the various areas across documents
+    self.state = {
+        page = nil,
+        pos = 0,
+        zoom = 1.0,
+        rotation = 0,
+        gamma = 1.0,
+        offset = nil,
+        bbox = nil,
+    }
+    self.highlight = {
+        lighten_factor = G_reader_settings:readSetting("highlight_lighten_factor", 0.2),
+        note_mark = G_reader_settings:readSetting("highlight_note_marker"),
+        temp_drawer = "invert",
+        temp = {},
+        saved_drawer = "lighten",
+        saved = {},
+        indicator = nil, -- geom: non-touch highlight position indicator: {x = 50, y=50}
+    }
+    self.page_states = {}
+    self.page_gap = {
+        -- color (0 = white, 8 = gray, 15 = black)
+        color = Blitbuffer.gray((G_reader_settings:readSetting("page_gap_color") or 8) / 15),
+    }
     self.visible_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
     self.page_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
     self.dim_area = Geom:new{x = 0, y = 0, w = 0, h = 0}
@@ -103,6 +105,9 @@ function ReaderView:init()
     self.emitHintPageEvent = function()
         self.ui:handleEvent(Event:new("HintPage", self.hinting))
     end
+
+    -- We've subclassed OverlapGroup, go through its init, because it does some funky stuff with self.dimen...
+    OverlapGroup.init(self)
 end
 
 function ReaderView:addWidgets()
@@ -1071,8 +1076,7 @@ function ReaderView:getRenderModeMenuTable()
 end
 
 function ReaderView:onCloseDocument()
-    self.hinting = false
-    -- stop any in fly HintPage event
+    -- stop any pending HintPage event
     UIManager:unschedule(self.emitHintPageEvent)
 end