Fetch Freetype source tarballs from a new host

[HexDecimal]

The old host is still unavailable. This is needed to fix build scripts and CI. Resolves #200

GitLab is picked over GitHub because of the archive format, GitHub only has zips.

tarfile.open call modified to use universal compression since there's no .tar.xz file available.

Test rexgex updated to understand the new source archive filename.

FreeType 2.13.2 accidentally pinned its CMake version to 3.0 which is no longer supported by CMake. -DCMAKE_POLICY_VERSION_MINIMUM=3.5 is added as a workaround and must be removed after updating FreeType.

[HinTak]

Your gitlab url is not a release tar ball but auto-generated ones against a tag. There is a small difference.

[HexDecimal]

I wouldn't argue otherwise. The main difference being how the archive file is labeled.

Is there a more important difference I'm missing? This is building from source as far as I can tell.

[HexDecimal]

FreeType doesn't do any GitHub releases or GitLab releases. The auto generated archives from tags appeared to be the next most reliable option.

[HexDecimal]

I'm willing to swap this to a different host URL if you have something in mind.

[HexDecimal]

I checked https://download.savannah.gnu.org/releases/freetype/ but the download was slow so I'm not confident it has the capacity for automated tasks. (could just be me though.) I misunderstood the nature of the mirror. It should be fine.

[HexDecimal]

I now replaced this with download.savannah.gnu.org so it should be the exact same file as before. (same SHA, same filename)

[HexDecimal]

The only thing remaining is the decision to to keep, revert, or erase my changes which allow for handling the auto-generated archives which are no longer downloaded by this PR.

The current host of this PR is FreeType's official meta-mirror: download.savannah.gnu.org found at https://freetype.org/download.html
I can't imagine a more authoritative source, other than the repos themselves.