Add glob() method for globs in favor of file()

[bentsherman]

Spawned from the language improvements mega-discussion (#3107). The file() method can be used to load a single file or multiple files using a glob string, which means this function can return a single path or a list depending on the input. This is bad. See #1236 and #2425 for similar problems.

Instead, there should be a separate function for globs, e.g. glob(), and the glob support via file() should be deprecated.

[pditommaso]

This already exists, it's called files 😄

https://github.com/nextflow-io/nextflow/blob/master/modules/nextflow/src/main/groovy/nextflow/Nextflow.groovy#L170-L173

[bentsherman]

If it's not in the docs then it doesn't exist!

[bentsherman]

Are you okay if we rearrange these functions so that file() throws a deprecation warning if you give it a glob?

[pditommaso]

It's a -1, this would mess up hundreds of pipelines for a problem can be solved just properly document file and files