Detect ManimGL version

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Closes #97

We detect the ManimGL version that the user is using. While in theory this is just issuing the command manimgl --version, there is soo much more that we have to do to ensure a nice user-flow and to handle all kinds of errors and particular situations. See the code for more details. What matters for the caller is that we can now do this (don't forget the await ⚠):

if (!await hasUserMinimalManimVersion("1.7.2")) {
     return;
}

in order to require specific versions for some features, e.g. reloading or --autoreload.

This method also takes care of showing respective warning messages etc. As a bonus feature, we call the GitHub API and if it returns something valid back, we show the user what the latest release version of Manim is.

Users can also switch ManimGL versions without having to reload VSCode. You just have to use the command Redetect Manim version. I've also removed the check manim version command from the walkthrough and instead use that new Redetect Manim version command there.

Refactoring

Since we needed some terminal-related methods also in a new file, I moved those methods from the Manim Shell to a new Terminal utility class.

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@bhoov Feel free to already play a bit around with these changes and check if many different scenarios work for you (e.g. also clicking away from a pop-up and trying to outsmart the logic I've written).

With regards to the code, I might do some more refactoring (of my newly written code) before I turn the draft PR to a regular one that can be reviewed.

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As I plan to refactor some code and lint it, I'm merging this now. Feel free to open issues if something is not working with it or if you don't like how I realized the version detection.