Improve PHPCS configuration

This commit implements the following changes to PHPCS execution via its configuration file:

- Show progress while it is running
- Improves performance by checking up to 8 files simultaneously
- Display only the relevant bit of filepaths when showing error and warnings

phpcs.xml

@@ -2,6 +2,8 @@
 <ruleset name="WordPress Coding Standards">
 	<description>WooCommerce dev PHP_CodeSniffer ruleset.</description>
 
+	<file>.</file>
+
 	<!-- Exclude paths -->
 	<exclude-pattern>tests/cli/</exclude-pattern>
 	<exclude-pattern>includes/libraries/</exclude-pattern>
@@ -13,6 +15,15 @@
 	<exclude-pattern>*/node_modules/*</exclude-pattern>
 	<exclude-pattern>*/vendor/*</exclude-pattern>
 
+	<!-- Show progress, show the error codes for each message (source). -->
+	<arg value="ps"/>
+
+	<!-- Strip the filepaths down to the relevant bit. -->
+	<arg name="basepath" value="./"/>
+
+	<!-- Check up to 8 files simultaneously. -->
+	<arg name="parallel" value="8"/>
+
 	<!-- Configs -->
 	<config name="minimum_supported_wp_version" value="5.0" />
 	<config name="testVersion" value="5.6-" />