Add explicit binding

[stefanoborini]

I thought I already filed this, but I cannot find it. Sorry if it's a reiterated request.

The problem we have with box is that the imported symbols are not explicitly bound. This angers linters, that see a symbol appear out of thin air and start complaining.

Example

box::use(mod/hello_world)

hello_world$hello('Ross')

This would trigger a linter problem because hello_world appears from nowhere.

I propose to support the additional syntax

hello_world <- box::use("mod/hello_world")

hello_world$hello('Ross')

This has the added benefit of allowing for easy renaming of the module in case of collision.

[caldwellst]

Second this, as I have to disable the OBJECT_USAGE_LINTER from {lintr} in codebases using {box} for this reason. However, wondering if support for box::use() syntax could be incorporated into {lintr} to maintain the current syntax, as I think that matches syntax extremely common in Python and many other languages.

[caldwellst]

r-lib/lintr#2060