[MOV] web: move FormView variables into the component folder

This commit moves the form variables from primary_variables.scss to
the FormView folder.

Part of the overall v16 SCSS optimization/restyle, task-2704984

task-2918464

Part-of: odoo/odoo#98101

addons/web/static/src/legacy/scss/primary_variables.scss

@@ -167,10 +167,6 @@ $o-kanban-mobile-empty-height: $o-kanban-image-width !default;
 // Used to manage spacing in complex dropdown menu
 $o-kanban-dashboard-dropdown-complex-gap: 5px !default;
 
-// Form view
-
-$o-form-view-sheet-max-width: 1140px !default;
-
 // Border-radius
 
 $o-border-radius: .25rem !default;

addons/web/static/src/views/form/form.variables.scss

@@ -0,0 +1 @@
+$o-form-view-sheet-max-width: 1140px !default;