[IMP] web: add decoration support for all field widgets (#25160)

It is sometimes useful to be able to customize slightly the color of a
field depending on some conditions on the current record.

For example, imagine that we want to show a VAT number field in green/red, if
it was validated or not. To do that, we can add a field with an
onchange, and simply add decoration-danger and decoration-success
attributes to the field.

doc/reference/javascript_reference.rst

@@ -1358,6 +1358,34 @@ Let us mention the most important ones:
 - the field widgets can be used outside of a view.  Their API is slightly
   awkward, but they are designed to be standalone.
 
+Decorations
+-----------
+
+Like the list view, field widgets have a simple support for decorations. The
+goal of decorations is to have a simple way to specify a text color depending on
+the record current state.  For example,
+
+.. code-block:: xml
+
+    <field name="state" decoration-danger="amount &lt; 10000"/>
+
+The valid decoration names are:
+
+- decoration-bf
+- decoration-it
+- decoration-danger
+- decoration-info
+- decoration-muted
+- decoration-primary
+- decoration-success
+- decoration-warning
+
+Each decoration *decoration-X* will be mapped to a css class *text-X*, which is
+a standard bootstrap css class (except for *text-it* and *text-bf*, which are
+handled by odoo and correspond to italic and bold, respectively).  Note that the
+value of the decoration attribute should be a valid python expression, which
+will be evaluated with the record as evaluation context.
+
 Non relational fields
 ---------------------