Ensure memory-efficient high-level document symbol cache #944

* 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

test/solidlsp/bash/test_bash_basic.py

@@ -50,7 +50,7 @@ class TestBashLanguageServerBasics:
         assert greet_user_symbol is not None, "Should find greet_user function"
 
         if "body" in greet_user_symbol:
-            body = greet_user_symbol["body"]
+            body = greet_user_symbol["body"].get_text()
             assert "function greet_user()" in body, "Function body should contain function definition"
             assert "case" in body.lower(), "Function body should contain case statement"