Launch space invaders on space

[LilithHafner]

When triage was discussing JuliaLang/julia#33875, we discussed the prevalence of keyboard soup scattered across the ecosystem where different packages use different "magic keys" to launch repl modes. @oscardssmith mentioned "you can even press space for space invaders"

While several closed-minded triagers assumed he was joking, the merits of this keybinding are quite apparent

• Space is a clear mnemonic for space invaders
• The space bar is conveniently located in the center of the widely used BÉPO keyboard layout, and has a large surface area for user convince
• No self-respecting line of Julia code entered at the REPL begins with a space

This PR makes pressing space at an empty julia> prompt launch space invaders.

In theory, this could be implemented as a package extension with REPL. However, according to several peer reviewed studies (source), there is growing concern among the Julia community that compile and load times are getting too low. This has resulted in decreased operational readiness in sword fighting atop rolling chairs (c.f. https://xkcd.com/303/). In an effort to rectify the situation, I didn't bother implementing this as a package extension.

As for the file name, while ".jl" is a classic ending, I think we can all agree that " .jl" is a bad file name, so I picked something a little more plain.

[oscardssmith]

lgtm.

[theogf]

Tested and approved!

[adrhill]

This needs a release asap!

Can we document it in the README? Maybe we don't need to, since it's such an intuitive feature in the first place.

[theogf]

JuliaRegistries/General#105025 (comment)

[ericphanson]

it's not allowed on windows apparently, so we don't allow it

[kellertuer]

Oh, that is sad, then even .jl would not help for that file. Maybe 👾.jl then?