refactor(path)!: support RFC3986 in path_with_url() #36564

Problem:
Nvim does not recognize URI scheme with numeric characters. While rare, there
are URIs that contain numbers (e.g. [ed2k://](https://en.wikipedia.org/wiki/Ed2k_URI_scheme))
and characters like `+` (e.g. `svn+ssh`). I use it in
[distant.nvim](https://github.com/chipsenkbeil/distant.nvim) to support
multiple, distinct connections using `distant+1234://` as the scheme.
Otherwise, if you open a file with the same name & path on two different
machines from the same Nvim instance, their buffer names will conflict
when just using `distant://`.

Solution:
Adds full support for detecting URI scheme per
[RFC3986](https://www.rfc-editor.org/rfc/rfc3986#section-3.1)

test/old/testdir/test_buffer.vim

@@ -445,12 +445,18 @@ func Test_buffer_scheme()
   set noshellslash
   %bwipe!
   let bufnames = [
-    \ #{id: 'ssb0', name: 'test://xyz/foo/ssb0'    , match: 1},
-    \ #{id: 'ssb1', name: 'test+abc://xyz/foo/ssb1', match: 0},
-    \ #{id: 'ssb2', name: 'test_abc://xyz/foo/ssb2', match: 0},
-    \ #{id: 'ssb3', name: 'test-abc://xyz/foo/ssb3', match: 1},
-    \ #{id: 'ssb4', name: '-test://xyz/foo/ssb4'   , match: 0},
-    \ #{id: 'ssb5', name: 'test-://xyz/foo/ssb5'   , match: 0},
+    \ #{id: 'ssb0' , name: 'test://xyz/foo/ssb0'    , match: 1},
+    \ #{id: 'ssb1' , name: 'test1234://xyz/foo/ssb1', match: 1},
+    \ #{id: 'ssb2' , name: 'test+abc://xyz/foo/ssb2', match: 1},
+    \ #{id: 'ssb3' , name: 'test-abc://xyz/foo/ssb3', match: 1},
+    \ #{id: 'ssb4' , name: 'test.abc://xyz/foo/ssb4', match: 1},
+    \ #{id: 'ssb5' , name: 'test_abc://xyz/foo/ssb5', match: 0},
+    \ #{id: 'ssb6' , name: '+test://xyz/foo/ssb6'   , match: 0},
+    \ #{id: 'ssb7' , name: 'test+://xyz/foo/ssb7'   , match: 0},
+    \ #{id: 'ssb8' , name: '-test://xyz/foo/ssb8'   , match: 0},
+    \ #{id: 'ssb9' , name: 'test-://xyz/foo/ssb9'   , match: 0},
+    \ #{id: 'ssb10', name: '.test://xyz/foo/ssb10'  , match: 0},
+    \ #{id: 'ssb11', name: 'test.://xyz/foo/ssb11'  , match: 0},
     \]
   for buf in bufnames
     new `=buf.name`