Add pre_resource_eval to POSIX provider

This commit adds API documentation, updates a call to, and adds a spec test for
the pre_resource_eval class function in the POSIX file provider (which was added
in puppetlabs#9349). When called, pre_resource_eval will create a class variable,
selinux_handle, which can be used when handling data for SELinux. Since the
handle is a class variable, we can avoid running into performance issues since
the handle can be re-used instead of needing to make a new one each time.

Additionally, since the old method wasn't completely removed & replaced
(and instead deprecated), less changes to old spec tests are needed as their
calls to the deprecated method aren't impacted.

lib/puppet/provider.rb

@@ -592,6 +592,14 @@ def <=>(other)
   # @return [void]
   # @api public
 
+  # @comment Document pre_resource_eval here as it does not exist anywhere else
+  # (called from transaction if implemented) @!method self.pre_resource_eval()
+  # @abstract A subclass may implement this - it is not implemented in the
+  # Provider class This method may be implemented by a provider in order to
+  # perform any setup actions needed, such as creating a handle. It will be
+  # called at the beginning of the transaction if the provider has implemented
+  # the method @return [void]
+
   # @comment Document post_resource_eval here as it does not exist anywhere else (called from transaction if implemented)
   # @!method self.post_resource_eval()
   # @since 3.4.0

spec/unit/transaction_spec.rb

@@ -420,6 +420,19 @@ def generate
       transaction.evaluate
     end
 
+    it "should call ::pre_resource_eval on provider classes that support it" do
+      skip if Puppet::Util::Platform.windows?
+      selinux = double('selinux', is_selinux_enabled: true)
+      stub_const('Selinux', selinux)
+
+      resource = Puppet::Type.type(:file).new(:path => make_absolute("/tmp/foo"))
+      transaction = transaction_with_resource(resource)
+
+      expect(resource.provider.class).to receive(:pre_resource_eval)
+
+      transaction.evaluate
+    end
+
     it "should abort the transaction on failure" do
       expect(resource).to receive(:pre_run_check).and_raise(Puppet::Error, spec_exception)