[CodingStyle] Fix NewlineBeforeNewAssignSetRector false positive on local var and $this property name collision

[TomasVotruba]

Fixes #8534

When a local variable and a class property share the same name, resolveCurrentStmtVariableName() resolved both to the same bare string. A $this->query assign returned the property name query, colliding with a local $query variable.

$query = [];                                    // resolved: query
$this->query = \is_array($query) ? $query : []; // resolved: query  <- collision
$this->another = 'string';                      // resolved: another

Two consecutive same-name entries then tricked the grouping into inserting a blank line before the next statement.

Fix: namespace the $this property result as this->property, so it can no longer match a local variable of the same name. Real runs of the same property still group correctly.

[TomasVotruba]

This should be fixed as variable and property name are not the same logical concept.