Rename Views method get_formula() to getFormula()

baldwinlouie and I are taking this.

Here's a patch.

#2: 2002916-rename-get_formula.patch queued for re-testing.

+++ b/core/modules/views/lib/Drupal/views/Plugin/views/argument/Date.phpundefined
@@ -92,11 +92,11 @@ function get_sort_name() {
+  function getFormula() {

+++ b/core/modules/views/lib/Drupal/views/Plugin/views/argument/Formula.phpundefined
@@ -38,7 +38,7 @@ public function init(ViewExecutable $view, DisplayPluginBase $display, array &$o
+  function getFormula() {

+++ b/core/modules/views/lib/Drupal/views/Plugin/views/argument/String.phpundefined
@@ -175,7 +175,7 @@ function summary_query() {
+  function getFormula() {

Add public access modifier in front of the functions to adher to the new OOP standards.

Re-rolled with public.

Looks good to me now !

Committed 16c85ce and pushed to 8.x. Thanks!