Quick-fix for missing pom.xml

[jurgenvinju]

The errors now shown at the "module" keyword would get a "code action" associated that generates the right pom.xml at the right place.

Propose to implement this in steps:

• PR for code actions for Rascal files (first only associated with diagnostics)
• PR for specific code action for missing pom.xml
• PR for other code actions related to project setup.

Let's try to keep code analysis, generation and transformation actions as much as possible written in Rascal. Eat-your-own-dogfood is good for quality/testing but also communicates to users the potential of Rascal. For example, we could keep the current analysis in TS, but have the Commands executed by Rascal (exactly as in the DSL-parameterized LSP server).