bustDirCache on FileSystemRouter.reload & fix of dir_cache keys in windows

[Kapsonfire-DE]

What does this PR do?

When the structure of the routes directory for the FileSystemRouter changes, the reload function cant load it, because readDirInfo is cached. So I changed the code to recursively bust the dirCache.

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

I dont know how to write tests for this. Ive tested it locally.

Fixes #4522

[paperdave]

nice. at a glance this looks reasonable, but you should add a test case to cover changing directories

[Jarred-Sumner]

Can’t we bump the version number and then we don’t need to eagerly call bustDirCache?

[Kapsonfire-DE]

@Electroid it seems it didnt worked, since CI still said no changed files

[Kapsonfire-DE]

The key generation for dir_caches had a bug on windows.
Trailing slashes were removed but it was hardcoded to "/" - since Windows uses "\" the bustDirCache function in Windows did not work properly. I've changed it by moving the hardcoded to a constant defined before. the constant is set on comptime.
\ for windows
else
/

[paperdave]

will run tests but one nitpick