Fail packaging if a "files" pattern does not include any file

[hediet]

vsce package should fail here:

{
	"files": [
           "this-file-does-not-exists.txt"
        ]
}

It should also fail here:

{
	"files": [
           "this-folder-is-empty/**/*"
        ]
}

This will prevent countless of bugs that are very easy to run into.
There should be a flag --ignore-empty-files-patterns to disable this check.