Improve text selection functionality

- Make text selection easier and quicker by selecting text directly on long press, and using standard grip bars for changing the selection.
- Disable the drawer while selecting text.
- Fix problem with selecting snippets of text with wide unicode characters at start and end.
- Remove the "tap-screen" configuration option for a more common show keyboard behaviour when tapping the terminal.
- Do no longer map the back key to escape by default - but it's still possible to do by configuration.
- Add new hardware keyboard shortcut Ctrl+Shift+K for toggling soft keyboard visibility.

app/src/main/java/com/termux/terminal/TerminalRow.java

@@ -184,6 +184,7 @@ public final class TerminalRow {
 		mSpaceUsed += javaCharDifference;
 
 		// Store char. A combining character is stored at the end of the existing contents so that it modifies them:
+		//noinspection ResultOfMethodCallIgnored - since we already now how many java chars is used.
 		Character.toChars(codePoint, text, oldStartOfColumnIndex + (newIsCombining ? oldCharactersUsedForColumn : 0));
 
 		if (oldCodePointDisplayWidth == 2 && newCodePointDisplayWidth == 1) {