Java front-end prototype

[keyboardDrummer]

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

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

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