[IMP] base: advertise view's active behavior in <template> vs <record>

Upon updates, the `active` field of `ir.ui.view` behaves differently
depending on whether the view is defined by using the `<template>` tag
or the `<record>` tag.

When using `<record>`, it behaves like any other field and gets updated
with the new value (notice that for qweb view, you should rarely rely
on this as if users customized those views with the website builder,
they are duplicated (COW)... updating the active field without migration
script would then be a source of errors).
When using `<template>`, it is not updated since [1], except for new
records since [2].

This commit adds a comment to the `active` field to help developers find
out about this difference.

See this [discussion].

[1]: https://github.com/odoo/odoo/commit/2d296cb77922d33be2dc45b900191fac34bda429#diff-175c28787c272a219b9275f79262a48af9aa029e718f45077fd609737559e84eR803-R804
[2]: https://github.com/odoo/odoo/commit/f1c70d4cc943ac4eb81a85a9dc005de34cd2060a#diff-175c28787c272a219b9275f79262a48af9aa029e718f45077fd609737559e84eR801-R804
[discussion]: https://github.com/odoo/odoo/pull/104836#discussion_r1013155860



Related to task-2963840

closes odoo/odoo#105524

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>