* Introduce SymbolBody representation (compact), from which the
body can be reconstructed, rendering body computation lazy
* Introduce SymbolBodyFactory for the creation of such instances,
ensuring that instances created from the same factory share
the same file content, allowing the in-memory and on-disk caches
to have a significantly smaller memory footprint
* Change type of "body" key in UnifiedSymbolRepresentation to use
SymbolBody instead of str
* Adjust all usages of the "body" key
Dominik Jain