Transition to `main` branch

[clason]

Nvim-treesitter is in the process of graduating the main branch, so nvim-treesitter-textobjects needs to follow suit.

Warning

The main branches are incompatible rewrites, and you cannot mix-and-match! If you do not want to deal with breaking changes, pin both nvim-treesitter and nvim-treesitter-textobjects to the respective master branch, which will remain available (even if no longer updated).

Roadmap:

• Port testing infrastructure from nvim-treesitter (feat(tests): renovate testing infrastructure #776) and fix test failures
• Freeze the master branch
• Cherry-pick(!) query updates from master branch
• Set up (buffer-local) mappings through setup()
• Update documentation