CodeAction to create missing noNamespaceSchemaLocation and generate XSD that adheres to current XML

[xorye]

This issue is an extension to #691

#691 implements a new code action to create a new missing XSD file with generic content (prolog). This issue is to improve upon this, by generating XSD that adheres to the newly created XSD file's corresponding XML.

[angelozerr]

For your information, @xorye I have started to experiment to generate XSD from XML files and DTD from XML files. See my branch at https://github.com/angelozerr/lemminx/tree/grammar-generator2

[angelozerr]

Fixed with #778