Fail Macro Expansion if JavaStaticField is used in non-class

[jrosen081]

Closes #65

This adds support for failing macro expansion if JavaStaticField is used in the incorrect context.

One thing I was thinking is we can add similar logic for the JavaStaticMethod to fail in that context. That will fail in compilation, but it could be nicer to fail expansion vs fail in an implementation detail (of a function not existing on the type)

[ktoso]

looks good, minor comment

[ktoso]

Tests failed, something isn't quite right:

/__w/swift-java/swift-java/Sources/JavaKit/generated/JavaBoolean.swift:31:3: error: Cannot use @JavaStaticField outside of a JavaClass instance (from macro 'JavaStaticField')
29 | }
30 | extension JavaClass<JavaBoolean> {
31 |   @JavaStaticField(isFinal: true)
   |   `- error: Cannot use @JavaStaticField outside of a JavaClass instance (from macro 'JavaStaticField')
32 |   public var TRUE: JavaBoolean!
33 | 

[jrosen081]

Tests failed, something isn't quite right:

/__w/swift-java/swift-java/Sources/JavaKit/generated/JavaBoolean.swift:31:3: error: Cannot use @JavaStaticField outside of a JavaClass instance (from macro 'JavaStaticField')

29 | }

30 | extension JavaClass<JavaBoolean> {

31 |   @JavaStaticField(isFinal: true)

   |   `- error: Cannot use @JavaStaticField outside of a JavaClass instance (from macro 'JavaStaticField')

32 |   public var TRUE: JavaBoolean!

33 | 

Oh my. I'm checking for classdecl, but I think I need to check for extensiondecl. I'll fix this up soon

[ktoso]

Nice, thank you very much!