Redesigned Add Shortcut Dialog Edit Box

The add shortcut dialog has a box where the users' selected key
combination is shown. Previously this box was just a clickable surface
that displayed some text/icon composable.

There are some downsides to this design:
1. No blinking cursor to show the user that they're currently editing.
2. A11y - No talkback actions on double click despite talback reading
   "double tap to activate"

The main consideration for not using a textfield composable previously
was that textfields can only show text, but keyboard keys can be
represented as text or glyphs(drawables) which traditional textfields
don't support.

This CL implements a custom InputField composable `OutlinedInputField`
which has all the benefits of a text field(blinking cursor, A11y
features) but rather than displaying just text, it generally supports
displaying any composable content which can be text, icon, or anything
else.this solution hence addresses both Downsides to the previous
design.

Test: Manual - Ensure the desired behaviour is observed in the add
shortcut dialog.
Flag: com.android.systemui.keyboard_shortcut_helper_shortcut_customizer
Fix: 390278358
Fix: 390102227
Fix: 390281127
Bug: 387995731

Change-Id: Ic5af2c9ba06a8cd0c204f742804d6202f2043e8a