add option to display syntax tree path in status line or enably sticky scroll

[calbaker]

Make it so that the [editor.statusline] section of config.toml could have something like center = ["file-name", "syntax-tree-path"] where the presence of "syntax-tree-path" would tell helix to display something like crate::mymod::MyStruct::my_method if my cursor is inside the function signature or body of my_method. This would have a similar effect to VS Code's sticky scroll. Another option would be to just implement VSCode's sticky scroll because it seems doable in Helix.

[calbaker]

Note that maybe syntax-tree-path is not the semantically correct name, and it's ok to change that to something more appropriate. I'm a mechanical engineer pretending to be a computer scientist.

[kirawi]

Duplicate of #396