Add package command for CMake.

[jehelset]

Adds support for package commands in cmake-projects. Both preset and non-preset version included.

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• The commits are consistent with our contribution guidelines
• You've added tests (if possible) to cover your change(s)
• All tests are passing (eldev test)
• The new code is not generating bytecode or M-x checkdoc warnings
• You've updated the changelog (if adding/changing user-visible functionality)
• You've updated the readme (if adding/changing user-visible functionality)

Thanks!

[bbatsov]

Thanks!