Make g.os_path_normslashes a do-nothing in leoJS

[edreamleo]

Leo PR #3241, merged into devel, contains non-controversial changes to Leo as part of Leo issue #3235.

Within Leo itself, g.os_path_normslashes translates backslash to forward slashes, but only on Windows. Imo, g.os_path_normslashes should be a do-nothing method on leoJS:

• There is no obvious reason why the hack in g.os_path_normslashes should be necessary, even on Windows.
• Messing with os.sep might (as an edge case) invalidate otherwise valid file specs.
• At present, making g.os_path_normslashes causes weird problems in Leo's Qt drawing code, but these weird problems do not justify propagating the hack to leoJS.
• leoJS should follow vs-code's handling of (external) files: leoJS should treat Windows file specs differently only if vs-code explicitly does so.

Summary

• The hack in g.os_path_normslashes is non-intuitive and troubling. I would like to remove it from Leo.
• leoJS need not (should not!) contain the same hack. Now it the best time to make g.os_path_normslashes a do-nothing in leoJS.
• In leoJS, adding calls to g.os_path_normslashes per Leo PR #3241 would encapsulate the dubious code to a single method. Comments in g.os_path_normslashes can discuss and justify the difference between Leo and leoJS.

[edreamleo]

@boltex I have changed my mind g.os_path_normslashes can remain as it is. The choice is yours.

We can rationalize the behavior of g.os_path_normslashes by saying that it converts paths to POSIX. I'm not sure how convincing that rationalization is, but I'll close this issue for now.