Partially addresses issue microsoft#27759

Adds compareFileNamesNumeric() and compareFileExtensionsNumeric()
funcitons, and uses the new functions in explorer view.

Fixes the following edge cases:

1. Sorts the same name with different case in locale order (a < A) instead of
unicode order (A < a).
2.  Sorts the same name with different accents or diacritics by locale
(á < à) instead of in unicode order (à < á) .
3. Sorts names that are equivalent in a numeric locale comparison
as shortest numeric representation first (1 < 01 < 001) instead of
unicode order (001 < 01 < 1).
4. For filenames with a name plus an extension, compares names first
fand then compares extensions (aggregate.go < aggregate_repo.go)
instead of comparing the whole name at once
(aggregate_repo.go < aggregate.go)
5. Treats dotfiles (filenames that start with a dot) as filenames
without extensions, instead of either as an empty filename plus
an extension (single-dot dotfile), or a filename that starts with a
dot plus an extension (multi-dot dotfile).  This means all dotfiles
group together in their own section when sorting by file type,
(.eslintignore < .eslintrc.json < file.cs < file.js < file.json) instead
of being interspersed between files grouped by type
(file.cs < .eslintignore < file.js < .eslintrc.json < file.json).

Note: other areas of workbench may benefit from the new functions
as well but only explorer has been changed so far.