Enhance loading during tapioca gem

[KaanOzkan]

bin/tapioca gem X loads all the gems but it only regenerates RBIs for X. This could cause issues when X RBIs rely on definitions from another gem, Y. An example of this is in spoom v1.2.2 (X) where there's a new method override that'll be generated in spoom's new RBIs. The abstract method is defined in syntax_tree gem(Y).

A problem occurs if loading of the abstract method has started after we last generated RBIs for syntax_tree. The abstract method isn't defined in syntax_tree's RBIs and we end up with a typechecking error.

We could implement @paracycle's suggestion from #1562 (comment)

• Track references to external constants
• Identify which gems the constants belong to
• Queue RBI generation for those gems.