[FIX] web_editor: position powerbox correctly in rtl direction

Issue:
======
The powerbox keep increasing in size when you input.

Steps to reproduce the issue:
=============================
- Install arabic
- Go to notes
- write `/`, you can see the powerbox is a bit smal
- use `down/up`arrows to navigate in the powerbox.
- The powerbox width increase until finally gets to it's intended
  position.

Origin of the issue:
====================
Since we are providing that `marginRigh` should be equals to `20` in
`getRangePosition` we will move the powerbox to the left a bit and then
with the style property `max-width=100%` it will increase in size
because the current size is a bit small for it. So at every key pressed
it will increase by 20px until it gets to a point where everything is
set and the `marginRight=20` is finally visible.

Soltuion:
=========
We set min-width as max-content so we can position correctly the
powerbox knowing it's final width.

task-3721794

closes odoo/odoo#161924

X-original-commit: b815447bf239049b37a3705cd014c67e3897ba9c
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Signed-off-by: Mahdi Cheikh Rouhou (macr) <macr@odoo.com>

addons/web_editor/static/src/js/editor/odoo-editor/src/style.scss

@@ -336,6 +336,7 @@
     max-height: 40vh;
     box-sizing: border-box;
     box-shadow: $box-shadow;
+    min-width: max-content;
 
     ::-webkit-scrollbar {
         background: transparent;