ui: Read custom recovery UI values via system property.

The matching change to build system now writes these values as build
properties for recovery image. This allows us dropping the dependency on
Android.mk (as well as having more flexibility to do UI customization).

Also rename a few constant names, as the naming doesn't fully follow the
style guide (which reads "whose value is fixed for the duration of the
program").

Bug: 110380063
Test: Build and flash recovery image on taimen, which uses custom margin
      height. Check the UI and choose `Run graphics test`.
Change-Id: I2c50326123639cb36022f51b62cdeed925d77ba7
diff --git a/wear_ui.h b/wear_ui.h
index c9a9f0e..b80cfd7 100644
--- a/wear_ui.h
+++ b/wear_ui.h
@@ -30,11 +30,11 @@
 
  protected:
   // progress bar vertical position, it's centered horizontally
-  const int kProgressBarBaseline;
+  const int progress_bar_baseline_;
 
   // Unusable rows when displaying the recovery menu, including the lines for headers (Android
   // Recovery, build id and etc) and the bottom lines that may otherwise go out of the screen.
-  const int kMenuUnusableRows;
+  const int menu_unusable_rows_;
 
   void StartMenu(const std::vector<std::string>& headers, const std::vector<std::string>& items,
                  size_t initial_selection) override;