[FIX] web_editor: apply font size on selected cells

Before this commit:

-Font size does not get applied to selected cells.
-Font style buttons were active when cells are selected.

After this commit:

-Font size can be applied.
-The font styles should not all be toggle by default.

task-3477490

closes odoo/odoo#133188

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>