[tvOS] Set `switches::kContentShellUserDataDir`

This CL sets `switches::kContentShellUserDataDir` to `base::DIR_CACHE`
in order to launch content shell, since local storage is limited on tvOS
and other directories are not allowed to write data.

It also moves handling `switches::kContentShellUserDataDir` from
`ShellBrowserContext::InitWhileIOAllowed` to `ShellPathProvider` so that
`SHELL_DIR_USER_DATA` can be accessed before `ShellBrowserContext`
creation.

And, shell_paths.{cc,h} are moved from content/shell/browser to
content/shell/common as //extensions also accesses
`SHELL_DIR_USER_DATA`.

Bug: 391914246
Change-Id: I2bf13aa8e6c280558be379c8e4391447727fd0d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6480975
Commit-Queue: Julie Jeongeun Kim <jkim@igalia.com>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Owners-Override: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1458691}