Problem:
- `vim.fs.abspath('fugitive:///a')` returns "<CWD>/fugitive:/a", so
filetype functions get a mangled path for URI buffers.
- `vim.fs.root()` doesn't accept "file://" URIs.
- No URI parser, so modules use ad-hoc scheme patterns, e.g.
`vim.ui.open('~/a:b')` treats the path as a URL.
Solution:
- Introduce `vim.uri.parse()`, and use it everywhere.
- DWIM: a one-letter "scheme" is a drive letter.
- `vim.fs.abspath()` returns URLs as-is.
- Expose `vim.uri` a module. Deprecate the old `vim.uri_xx()` names.
Justin M. Keyes
5a37eb7a49