Upstream meson lsp

This is the integration for Swift-MesonLSP.

I'm not sure, what you describe as "insane to build", but I can list the facts about the build process. (In the end it's probably more like the other language servers - like e.g. ts-language-server -, that require you an enduser to install the language server, as I highly doubt, you want to ship a 60-100MB binary. Especially as basically there is nearly? no precedent in many distributions, how to package a Swift application.)

Facts:

• It's really a standard swift build. You need the toolchain. (Either from https://www.swift.org/ or from your package repos like swift-lang on Fedora)
• Just do swift build -c release --static-swift-stdlib. The binary will have the swift stdlib/Foundation linked, as otherwise that would require having those libraries on the host. (A Makefile for the default make&&sudo make install is provided for convenience)
• It is not possible to build in Flatpak currently, as there is no Swift toolchain anywhere
• Even if there would be a Swift toolchain, setting up an offline build would require a bit more setup. (Comparable to this: https://github.com/JCWasmx86/org.freedesktop.Sdk.Extension.swift/blob/main/swift-format-setup-offline.sh)
• Release build takes around 10-15 minutes

Fixes #629 (closed)