(#13737) Swap build_tree and format_tree method names

The Puppet::Module::Tool.build_tree and
Puppet::Module::Tool.format_tree method names do not match their
behavior. Both methods actually do the inverse,
Puppet::Module::Tool.build_tree formats a tree for output and
Puppet::Module::Tool.format_tree builds the tree that is passed to
Puppet::Module::Tool.build_tree. Even this commit message is
confusing.

This patch swaps the names and updates the related specs.