[FIX] web_editor: BS4 input group button height glitch

As an `form-group` can contains element having `form-control` class and other
not having it, we should not force height on `form-group` elements.

Typically, we could have:
div.form-group
  input.form-control
  button

Forcing height only on `form-control` will make the input thinner than the
button.

addons/web_editor/static/src/scss/web_editor.variables.scss

@@ -101,8 +101,10 @@ $o-we-switch-inactive-color: $o-we-color-paper !default;
 }
 
 @mixin o-w-preserve-forms {
-    .form-control {
+    :not(.input-group):not(.form-group):not(.input-group-append):not(.input-group-prepend) > .form-control {
         height: 34px;
+    }
+    .form-control {
         padding: 6px 12px;
         font-size: 14px;
         line-height: 1.5;

addons/web_editor/static/src/xml/editor.xml

@@ -85,7 +85,7 @@
             <input t-if="widget.options.res_id" type="hidden" name="res_id" t-att-value="widget.options.res_id"/>
             <input t-if="widget.options.res_model" type="hidden" name="res_model" t-att-value="widget.options.res_model"/>
             <div class="card">
-                <div class="card-body">
+                <div class="card-body p-0">
                     <div class="form-inline">
                         <input type="file" class="d-none" name="upload" t-att-accept="widget.accept" multiple="multiple"/>
                         <input type="hidden" name="disable_optimization" value=""/>