Redesign custom canonicalize, enable multiple dots expansion earlier. (#1588)

* Expand n dots early where tilde was also expanded.

* Remove normalize, not needed.
New function absolutize, doesn't follow links neither checks existence.
Renamed canonicalize_existing to canonicalize, works as expected.

* Remove normalize usages, change canonicalize.

* Treat strings as paths

crates/nu-parser/src/lib.rs

@@ -1,6 +1,7 @@
 mod files;
 mod lite_parse;
 mod parse;
+mod path;
 mod shapes;
 mod signature;