Improve project detection algorithm using salsa crate

[pfoerster]

This PR improves the current project detection algorithm used to build a dependency graph and load the missing files from the disk. It uses the salsa crate (salsa-2022 to be exact) and fixes many long-standing bugs:

• Fixes Where are the compilation errors? #491
• Fixes Build On Save #502
• Fixes No compilation error updates in diagnostics unless I restart texlab in Neovim #679
• Fixes Wrong file built in a directory with multiple main files #757
• Fixes Texlab compiles the wrong tex file and opens the wrong pdf #806
• Fixes Autocomplete on citation title, authors, etc #829
• Fixes LaTeX error: \usepackage before \documentclass #801

A more detailed changelog can be seen here: https://github.com/latex-lsp/texlab/blob/salsa/CHANGELOG.md#unreleased

In particular, the meaning of texlab.rootDirectory has changed:
Consider the following project structure:

| project
|-- src
    |-- main.tex
|-- build
    |-- main.pdf
    |-- main.log
    |-- main.aux

Then you need to set texlab.rootDirectory to ".." and texlab.auxDirectory to build. As a consequence, texlab no longer depends on the working dir passed to the process.