Checks if a file exists (using validate_file()) and it is a valid WordPress plugin file (using get_plugins())
- (string) (required) The path of the plugin file relative to WP_PLUGIN_DIR.
- Default: None
- Return 0 on success and WP_Error on failure with any of the following messages.
- Invalid plugin path.
- Plugin file does not exist.
- The plugin does not have a valid header.
validate plugin() is located in