[FIX] base: correctly define `arch` as depending on context

Computed fields that depend on the context now have to be declared as such.

To reproduce the issue:
- go on the form view of any view
- update the arch of the view
- save
- click on action "reset view architecture"
- select hard reset
- no diff is shown

Expected: a diff should be shown

`arch_base` depends on `arch`, so even though no current flow actually uses it
when the context is changed, update its `depends_context` as well to be safe.

closes odoo/odoo#38536

Pr: #37363
X-original-commit: be658bb8
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>