feat(treesitter): include parent tree in addition to injected tree for Treesitter node selections

[atusy]

I often have a situation where I want treesitter node selections to select outside the injections.

Here's a screenshot from :lua require("flash").treesitter({ highlight = { backdrop = true } }) in a markdown code block.

Note that the similar features are available in https://github.com/ggandor/leap-ast.nvim and https://github.com/mfussenegger/nvim-treehopper .