Adds foreground and background layers

- in onKeyDown() return false when the key is not handled.

The above two changes fix the handling of Fn-key combo's on devices with
a physical keyboard, allowing the android system defined fallbacks from
`/system/usr/keychars/Generic.kcm` to be properly handled.

Fixes #731.

Original diagnosis and fix by Konehaltia.

app/build.gradle

@@ -13,8 +13,8 @@ android {
         applicationId "com.termux"
         minSdkVersion 21
         targetSdkVersion 27
-        versionCode 64
-        versionName "0.64"
+        versionCode 65
+        versionName "0.65"
     }
 
     buildTypes {

app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@mipmap/ic_background"/>
+    <foreground android:drawable="@mipmap/ic_foreground"/>
+</adaptive-icon>

terminal-view/src/main/java/com/termux/view/TerminalView.java

@@ -600,7 +600,7 @@ public final class TerminalView extends View {
         if (controlDownFromEvent) keyMod |= KeyHandler.KEYMOD_CTRL;
         if (event.isAltPressed()) keyMod |= KeyHandler.KEYMOD_ALT;
         if (event.isShiftPressed()) keyMod |= KeyHandler.KEYMOD_SHIFT;
-        if (handleKeyCode(keyCode, keyMod)) {
+        if (!event.isFunctionPressed() && handleKeyCode(keyCode, keyMod)) {
             if (LOG_KEY_EVENTS) Log.i(EmulatorDebug.LOG_TAG, "handleKeyCode() took key event");
             return true;
         }
@@ -619,7 +619,7 @@ public final class TerminalView extends View {
         if (LOG_KEY_EVENTS)
             Log.i(EmulatorDebug.LOG_TAG, "KeyEvent#getUnicodeChar(" + effectiveMetaState + ") returned: " + result);
         if (result == 0) {
-            return true;
+            return false;
         }
 
         int oldCombiningAccent = mCombiningAccent;