(#13682) Rename Puppet::Module::Tool to Puppet::ModuleTool

Without this patch, Puppet will monkey patch the existing implementation
of the puppet-module Gem if it is used. This is bad because the two
implementations are all jumbled up inside of one another and behavior
may become unpredictable. Warnings are also displayed directly to the
end user in the form of redefined constants.

This patch fixes the problem by renaming Puppet::Module::Tool inside of
Puppet to Puppet::ModuleTool This fixes the problem because Puppet will
no longer monkey-patch the Puppet::Module::Tool module inside of the
puppet-module Gem.

This patch also has the added benefit of making the Module's name match
up with the CamelCase filepath (puppet/module_tool/ =>
Puppet::ModuleTool) As a result, no file moves are necessary.