This is a squashed commit that includes:
Replace cgo Condition in Go Config
Include WebTunnel README in Browser
Include WebTunnel into Tor Expert Bundle
Add WebTunnel to default torrc
Add WebTunnel project

Their original form is available at:
https://gitlab.torproject.org/shelikhoo/tor-browser-build-2/-/commits/dev-webtunnel-rebased-backup

See also: !595

updated rbm submodule to use gitlab url

In input_files in projects/firefox-l10n/config we are doing this:

  my $locales = project_config($project, 'var/locales', $options);
  foreach my $locale (@$locales) {
    $locale = process_template($project, $locale, '.');

In this foreach loop, `$locale` is pointing to the real string from
`var/locales` and not a copy, and we are updating it with the output
from `process_template`. This means that the template will be processed
the first time the function is called (for example for a linux-x86_64
build) and the processed value from the first call reused on subsequent
calls (for example a macos build, where the `ja` locale is supposed to
be different).

This is what caused the reproducibility issue in
tpo/applications/tor-browser-build!591 (comment 2857042)

To fix that we just use a separate variable to store the processed
template.

We also add android download json files (#40110).

Initially we thought of not creating a branch for base-browser, but only
a tag. However, fixing trivial issues for the base-browser part needed
a rebase in this way, if they were needed to correct the nightly.
So, we decided to create a branch also for base-browser.

Disable updater in base-browser to avoid it getting updated to firefox.

The previous way we were using to merge locales in the builds worked
with Linux and Windows, but not with macOS.

We are adding a notification to tell users they can change their
language. It needs new strings, and I have decided to use Fluent for
them, for a series of reasons.

However, it is the first component to use Fluent, and it needs to be
translated with Weblate, but we are not moving base-browser to Weblate,
yet.
So, we are using another branch on translation.git and we need a new
project to fetch it, which I am adding with this commit.

Also, I have changed how we manage base-browser translations, and
transformed the TT for to a bash for, to keep the Firefox build script
shorter, which is helpful for build debugging sessions.

`make torbrowser-testbuild-macos-x86_64`
  and
`make torbrowser-testbuild-macos-aarch64` can be used to do non-universal
testbuilds for a single arch.

The new macos mar and dmg files contain both x86_64 and aarch64 builds
for macOS.

In projects/release/update_responses_config.yml and
tools/signing/nightly/update-responses-base-config.yml we update the
build_target to mar_osname mapping to use `macos` instead of `osx64`.
We also add the new aarch64 build_target (Darwin_aarch64-gcc3).

We update update_responses to take into account the new dmg file
names using `macos` instead of `osx64`.

We also update tools/dmg2mar and various signing scripts for the
`osx64 -> macos` change in both mar files and dmg files.

Instead of having separate x86_64 and arm64 macos builds, we merge the
two builds to create an universal build, using the unify.py script from
Mozilla.

We also start renaming osx64 to macos for tor-browser-build#40067.

fixup for 98b4184d.

Do not use firefox-l10n in testbuilds, since it is not available.

Use our own copy of the repo that includes uTLS support.

Since we have packaged locales, we do not have to include language packs
anymore.

Also, we have decided that we are not switching back from multi-lingual
packages, so we remove the support to single-lingual packages to
simplify the browser project.

This commit changes Firefox build script to run the needed steps to
include additional locales as packages locales.

In our first tests, adding a locale adds at least 10 seconds to the
build, so we do not add locales for testbuilds.

We do not bundle HTTPS Everywhere anymore, so we do not need to add it
to local builds anymore.

Removed mingw-w64 as a depdency from Firefox, since we take libssp
directly from mingw-w64-clang (the default compiler for Windows now).

Also, take clang as a depdendency for Firefox only on Linux, since
macOS and Windows contain it in their compiler packages.

This reverts the changes from 3a12465d
to that file.

Since we changed in a3f49129 the default
locale to be `ALL`, users of any unkwnown locale should now be redirected
to `ALL`, without the need for setting `migrate_langs` for those
locales.