Add TLS and HTTPS support

[binary1248]

This change adds support for Transport Layer Security to sf::TcpSocket using Mbed TLS.

Because HTTPS is just HTTP over a TLS stream, support for HTTPS was also added.

All of the existing sf::TcpSocket interfaces stayed the same. After a connection is established on either client or server, the corresponding setup function has to be called. For clients setupTlsClient has to be called and for servers setupTlsServer has to be called. The arguments that have to be supplied are those typical of setting up any TLS stream.

For a usage example, the Sockets example was modified to give the user a choice of enabling TLS. Additionally, since HTTPS is also supported with this change, a HTTP example was added that can be used to connect to websites using HTTP/HTTPS.

Finally, connection tests were added for TLS and non-TLS TCP streams.

Since CI passes with the tests enabled on almost all platforms, it means the implementation including loading certificates from the system certificate store works on all those platforms. The only platform that is currently unsupported is iOS since Apple deliberately chose not to provide the same Security framework APIs as it does on macOS. After searching for a while I gave up thinking of how to load system certificates on iOS. If there are any iOS experts out there, they can try their luck adding a working implementation for it.

[Bambo-Borris]

Dang! Another great feature so soon. Looking forward to seeing this merged

[binary1248]

Rebased onto master.

[github-actions]

Pull Request Test Coverage Report for Build 18615251839

Details

• 309 of 412 (75.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.5%) to 59.647%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/SFML/Network/Http.cpp	7	8	87.5%
src/SFML/Network/TcpSocket.cpp	301	403	74.69%

Totals
Change from base Build 18483127964:	1.5%
Covered Lines:	13291
Relevant Lines:	21467

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💛 - Coveralls

[eXpl0it3r]

This looks great! 🥳

I added some questions and minor code structure comments, nothing to really block this PR further.

[binary1248]

Rebased onto master.

[learn-more]

Some notes / questions I had while reviewing the code.

[binary1248]

Updated.

[binary1248]

• Updated to Mbed TLS 3.6.5.
• FetchContent now downloads the release archive instead of performing a git shallow clone, the release archive contains pre-generated files that are necessary for the build
• Adopted changes from Disable warnings for harfbuzz and sheenbidi. Use block() for cmake scope #3625

[eXpl0it3r]

Another long awaited feature has landed in SFML! 🥳

Thank you for bringing TLS to SFML! ♥️