[IMP] website: add an aria-label on the extra item anchor

The goal of this commit is to add an `aria-label` attribute on the
"extra item" anchor in order to improve the accessibility of the website
pages and avoid a warning of type `Links do not have a discernible
name`. However, as the logic responsible of the creation of this anchor
is in a non lazy loaded file, the translate function `_t()` (located in
a lazy loaded file) can not be used to translate the value of the
`aria-label` attribute. To solve the problem, this value has been put in
the `data-extra-items-toggle-aria-label` attribute on the header. The
translated value is then extracted and added in the `aria-label`
attribute at the extra items button creation.

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[IMP] website: add a default meta description on website pages

The goal of this commit is to add a default meta description on website
homepage and "contact us" page in order to improve their SEO and avoid a
warning of type `Document does not have a meta description`.


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[IMP] website: add an aria-controls attribute on accordion tab elements

In order to improve the accessibility of the website pages, an
`aria-controls` attribute has been added on `tab` elements of the
"Accordion" snippet to avoid a warning of type `Elements with an ARIA
[role] that require children to contain a specific [role] are missing
some or all of those required children`. Indeed, as explained in
[the tab role documentation]; "An element with the `tab` role should
contain the `aria-controls` property identifying a corresponding
`tabpanel` (that has a `tabpanel` role) by that element's `id`". The
`_createIDs()` method has been adapted in order to handle the update of
the `aria-controls` attribute at the update of the `tabpanel` id.

[the tab role documentation]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/tab_role#description

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[IMP] website, *: add aria-label on social media anchors

*: website_hr_recruitment

In order to improve the accessibility of the website pages, an
`aria-label` attribute has been added on some social media anchors to
avoid a warning of type `Links do not have a discernible name`. The
`options.js` file has also been adapted in order to correctly set the
`aria-label` attribute of added social media anchors.

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[IMP] *: improve accessibility of website pages

*: base_import, gamification, hr_skills, mass_mailing, portal,
portal_rating, survey, web, web_editor, website, website_sale,
website_slides

The goal of this commit is to improve the accessibility of the website
pages. This has been made by implementing and correcting ARIA
(Accessible Rich Internet Applications) roles and attributes. More
precisely:
- An `aria-label` attribute has been added on progressbar elements to
avoid a warning of type `ARIA progressbar elements do not have
accessible names`. It has also been added on iframes to avoid a warning
of type `<frame> or <iframe> elements do not have a title`. Furthermore,
`aria-label` has been incorporated on some anchors to avoid a warning of
type `Links do not have a discernible name`. Finally, it has been added
on elements that have the `dialog` role to avoid a warning of type
`Elements with role="dialog" or role="alertdialog" do not have
accessible names` and on elements that have the `listbox` role to avoid
a warning of type `ARIA input fields do not have accessible names`.
- To avoid a warning of type `Some ARIA parent roles must contain
specific child roles to perform their intended accessibility functions`,
`role="menuitem"` has been added on children of menu elements. As
explained in [the menuitem role documentation], "The `menuitem` role
indicates the element is an option in a set of choices contained by a
`menu` or `menubar`". To avoid this warning, `role="presentation"` has
also been added on elements located between `tablist` and `tab` and
between `menu` and `menuitem`. Indeed, as explained in
[the presentation role documentation]; "The `presentation` role removes
an element's implicit ARIA semantics from being exposed to the
accessibility tree". The goal is to inform the assistive technologies
that the default semantics of the element should be ignored. Finally, to
avoid this same warning, the `option` role has been added on elements to
identify selections a user can make in a `listbox`.
- The `aria-label` of some elements has been adapted in order to avoid a
warning of type `Elements with visible text labels do not have matching
accessible names`.
- The value of `aria-disabled` has been corrected to `true` (instead of
`disabled`) (see [the aria-disabled documentation]).

Still to improve the accessibility of the website pages, an alternative
text (`alt`) attribute has been provided for images.

[the menuitem role documentation]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/menuitem_role
[the presentation role documentation]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/presentation_role
[the aria-disabled documentation]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Attributes/aria-disabled#values

Forward-Port-Of: odoo/odoo#140453