WP/AlternativeFunctions: fails to detect namespaced and class-based function/constant calls

The sniff WordPress.WP.AlternativeFunctions checks for function calls and constants in the first parameter of file_get_contents() without differentiating global and non-global function calls and constants. It also fails to differentiate between functions/constants, and class methods/class constants. This leads to false negatives in some cases.

All the examples below don't trigger the sniff, but they should:

file_get_contents(MyNamespace\WP_Upload_Dir()['path'] . 'subdir/file.inc');
file_get_contents(\MyNamespace\WP_Upload_Dir()['path'] . 'subdir/file.inc');
file_get_contents(namespace\WP_Upload_Dir()['path'] . 'subdir/file.inc');
file_get_contents(MyNamespace\ABSPATH . 'wp-admin/css/some-file.css');
file_get_contents(\MyNamespace\ABSPATH . 'wp-admin/css/some-file.css');
file_get_contents(namespace\ABSPATH . 'wp-admin/css/some-file.css');

file_get_contents(MyClass::wp_upload_dir() . 'subdir/file.inc');
file_get_contents($this->wp_upload_dir() . 'subdir/file.inc');
file_get_contents(MyClass::ABSPATH . 'subdir/file.inc');
file_get_contents($this->ABSPATH . 'subdir/file.inc');

Start at the WordPress.WP.AlternativeFunctions sniff and reproduce the listed file_get_contents() examples. Trace how its first parameter is classified, distinguishing namespaced and global functions/constants from class methods, class constants, and $this-> calls. Done when the examples trigger the intended detection without introducing false positives.