feat: support MSYS forward slashes with experimental flag

[pschiel]

WIP

issues:

• git rev-parse --show-toplevel returns E:/x/y forward slash format
• path.resolve(), path.relative(), realpathSync.native(), realpath (bash) break when git bash (msys) paths are used
  • /d/x within C drive (/c/) results in things like C:\d\x
  • relative paths not working like expected using cross-drive
  • some path matching issues (relative, contains, ..)
  • /tmp inside git bash is something else outside of it
• tools break using backslash paths (some backslashes get "eaten")
• escaping hell for agents
• observed in all win32 native shells

patch tries to fix:

• convert to forward slash format at all places where things break (tool calls and bash mostly)
• in Filesystem as wrapper functions (path.resolve -> Filesystem.resolvePath)
• configurable with flag (otherwise backslash paths are guaranteed - but still some bugs with these)

todo:

• clean up Filesystem functions (relativePath, overlaps, possibly add dirpath)
• add tests for Filesystem
• maybe change flag with SHELL detection
• test all tools, incl. permission checks