Avoid further processing when the XML file is not related to a tool wrapper file

[davelopez]

The language server extension gets activated by default when the user opens a file with .xml extension. It seems there is currently no way to activate the extension based on the contents (for example to differentiate a tool wrapper from some other random XML file).
One possible solution to this issue is to 'peek' the contents of the XML file and determine if this is actually a tool wrapper related file (tool, macros, etc.). If the XML file does not pass this check, all the language server requests will be discarded. The extension will still be active, but this will help avoid any further processing or errors trying to process a file that it's not meant to be analyzed.