[FIX] web: center image_field buttons

The buttons in image_field are not centered vertically. Since it's a
custom sized button, using flex is reliable (it's now centered on both
flex axis).

Note: Done in SCSS instead of utilities because the flex is there to
compensate the custom size set in SCSS (easier to maintain) + there
could be injected buttons in the component.

task-5258887

closes odoo#238449

X-original-commit: 55c8a5a
Signed-off-by: Aaron Bohy (aab) <[email protected]>
Signed-off-by: Mathieu Notté (mano) <[email protected]>

Author: mano-odoo

addons/web/static/src/views/fields/image/image_field.scss

@@ -16,6 +16,9 @@
 
     button {
         transition: opacity ease 400ms;
+        display: flex;
+        justify-content: center;
+        align-items: center;
         width: 26px;
         height: 26px;
     }