adminlib: get_component_version() does not always use the plugin manager

I discovered by accident that get_component_version() function in the adminlib.php does not use the plugin manager features designed exactly for this.

Additionally, it looks like this function is used at only three places at the moment. So, the suggestion is to:

• Rewrite the function so that it uses the plugin manager
• Rewrite all three places using it to use the plugin manager directly instead
• Deprecate and eventually remove this function completely