path: more small refactorings

1) Refactor for loops to while loops that were only meant to count
   up a variable.
2) Refactor some `var` statements to `let` / `const`.
3) Simplify return conditions.
4) Use template strings where possible instead of concat.
5) Use ternary expressions for variable assignments instead of
   if / else.
6) Use the object shorthand notation for the function declarations.
7) Consolidate if else case where possible.
8) Remove double line breaks.

PR-URL: https://github.com/nodejs/node/pull/25278


Reviewed-By: Michaël Zasso <targos@protonmail.com>