Prototype for adding a front-end for an extension of Java that supports verification.

Description

• The file JavaGrammar.cs contains the currently partial definition of the extended Java.
• The new project CompilerBuilder contains a DSL for defining grammars from which parsers and printers can be extracted. It still needs work to polish the API and it needs a cache to improve backtracking performance.
• ProgramParser.cs has been adopted so it calls the Java parser instead of the Dafny parser, based on the file extension.
• There are small changes to the DafnyLanguageServer project to indicate that it also support this extensions java language.
• There are small changes to the Dafny AST to accommodate how the grammar DSL currently works, but I expect to make this unnecessary

How has this been tested?

WIP

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