Edge cases of file path construction that aren't practical

[hiiamboris]

Describe the bug

1. When path is empty, adding a filename to it puts it into system root rather than current directory, which is a ground for gotchas. Majority vote (4:1) prefers current directory in this case:

>> path: %""
>> path/file.ext
== %/file.ext       ;) accidental root access

2. When added filename is an absolute path, resulting path is invalid. So a pattern that successfully adds relative path to the current directory fails if path is absolute:

>> path: %/D/devel/red/
>> boot: %./1.exe
>> path/:boot
== %/D/devel/red/./1.exe      ;) valid path to the binary
>> boot: %/D/devel/red/1.exe
>> path/:boot
== %/D/devel/red//D/devel/red/1.exe      ;) garbage out

It is understandable that / works simply as append dirize, but it requires higher level function wrapper to achieve this very common goal.

Similarly we may want to address these cases as well:

>> dirize %""      ;) will lead to root access
== %/
>> dirize clean-path %""
== %/C/Users/1/
>> clean-path dirize %""     ;) unexpected order-related difference
== %/

Expected behavior

>> path: %""
>> path/file.ext
== %file.ext

>> path: %/D/devel/red/
>> boot: %/D/devel/red/1.exe
>> path/:boot
== %/D/devel/red/1.exe

>> dirize %""
== %""
>> (dirize clean-path %"") = (clean-path dirize %"")
== true

Since there's no direct function equivalent of this behavior, there are multiple options:

1. Keep / simple but provide a function wrapper for path joining
2. Make / smarter
3. Make / smarter and add a function alias to it

I'm leaning towards (3). Note that append dirize equivalent cannot fulfill this case, requires more smarts:

>> path/:boot
== %/D/devel/red/1.exe

Platform version

Red 0.6.4 for Windows built 22-Nov-2023/17:24:25+03:00 commit #34f26df