Add typed properties for TypedPropertiesBag

[hpmellema]

Background

Adds a strongly typed Key to the typed properties bag used by Symbols in codegen. These changes are intended to improve the experience of using Symbol properties in code generators. Usage of these new typed properties would look like:

Property<String> myStringProperty = Property.named("string property"); 

Symbol symbol = Symbol.builder()
                .name("foo")
                .putProperty(myStringProperty, "foo")
                .build()
                
String result = symbol.expectProperty(myStringProperty);

Testing

Added new unit tests

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