add cache and main

[rohanmayya]

What does this PR do?

Added remaining types to Require's interface, cache and main.

Previously, in my own project, I could not do:
delete require.cache[filePath];

to clear my import cache, because cache was not a recognized type on require.

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

[Electroid]

thanks!