Problem:
vim.fs.normalize() normalizes too much vim.loader and is slow.
Solution:
Make it faster by doing less. This reduces the times spent in
vim.fs.normalize in vim.loader from ~13ms -> 1-2ms.
Numbers from a relative benchmark:
- Skipping `vim.validate()`: 285ms -> 230ms
- Skipping `path_resolve_dot()`: 285ms -> 60ms
- Skipping `double_slash`: 60ms -> 35ms
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