Use DLL to avoid recompiling all assets

[anatawa12]

When we imported VPAI, All assemblies are recompiled & reloaded so It took loooong time to install.
So, I want to change to dll to avoid this problem.

TODOs before implement this:

• check if using dll can avoid recompiling at the time imported: YES
• we can remove dll from dll
  • on windows (removing opened file is disallowed)
  • on macos (removing opened file is allowed)
• check if using dll can avoid recompiling after delete: NO, but because we can avoid at import, we can reduce time to import to about half so I still want to implement this