add Polyglot Modeling tools to Shape Convertors

[VladimirAlexiev]

• Polyglot Modeling w3c/yaml-ld#19 describes 20-25 tools that generate various technical artefacts from a common schema.
• merge 2 pairs of sections, add convertors (SchemaOps) #31 merges 2 sections to "Shape Convertors and Generators" and refers to the above list. It also describes maybe 5 tools from the list

Let's take a look at the remaining tools and decide which ones to include (of course, they should be able to work with SHACL and/or SHEX)