This change introduces a new security option for setting the SameSite
option to all cookies sent by TYPO3 Core.

Namely:
- Frontend User Sessions ("lax" by default)
- Backend User Sessions ("strict" by default)
- Install Tool Sessions ("strict", none-configurable)
- Last Login Provider in Backend ("strict", non-configurable)

This means that these can only be accessed by scripts and requests
by the same site, and not by any third-party scripts.

Since we're talking about actual cookies for a user, and not
ads-related or third-party login-dependant cookies, the default
options fit just perfectly.

All modern browsers except Internet Explorer respect this option
to be set. Please note that Firefox and Chrome will have "SameSite=lax"
set in Q1/2020 by default if NO SameSite option is set at all. This change
allows to configure this.

Backend and Frontend User Cookies can be configured to "strict", "lax"
or "none" (= same as before), whereas "none" only works for secure
connections (= HTTPS).

If "strict" is in place, security via CSRF is not needed anymore, and can
be dropped in the future.

Resolves: #90351
Releases: master, 9.5, 8.7
Change-Id: I8095e2a552faa9d1fd4fa7855297302a9ec6a75f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63183


Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>