Move MILL_MAIN_CLI handling before shifting arguments

[sake92]

I had an issue with BSP import on Windows, and after some debugging I think I found the bug here.

The MILL_MAIN_CLI was parsed after the arguments were shifted so %0 became %2 (the version parameter)

I added additional improvement, %~f0 (returns absolute path),
instead of just %0, which can be quirky.
https://stackoverflow.com/questions/35685721/batch-scripting-whats-the-difference-between-0-and-f0

Before:

.\.metals\millw.bat --mill-version 0.11.5 mill.bsp.BSP/install

cat .\.bsp\mill-bsp.json
{"name":"mill-bsp","argv":["0.11.5","--bsp","--disable-ticker","--color","false","--jobs","1"],"millVersion":"0.11.5","bspVersion":"2.1.0-M7","languages":["scala","java"]}

After:

.\.metals\millw.bat --mill-version 0.11.5 mill.bsp.BSP/install

 cat .\.bsp\mill-bsp.json
{"name":"mill-bsp","argv":["C:\\projects\\sake\\squery\\.metals\\millw.bat","--bsp","--disable-ticker","--color","false","--jobs","1"],"millVersion":"0.11.5","bspVersion":"2.1.0-M7","languages":["scala","java"]}

[lefou]

Looks good to me. Thank you @sake92 !