K2 Scripting: wrap script statements into blocks

(reuse anonymous initializers as block wrappers) so the top-level script
elements are all declarations now. Rename the property accordingly (
together with the previous commit).
It makes script more similar to the class and thus simplify e.g.
control flow analysis and resolve code.

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/symbols/pointers/KtFirScriptParameterSymbolPointer.kt

@@ -27,7 +27,7 @@ internal class KtFirScriptParameterSymbolPointer(
             scriptPointer.restoreSymbol()?.firSymbol?.fir as? FirScript
         } ?: return null
 
-        val parameter = script.parameters.find { it.name == parameterName } as? FirProperty ?: return null
+        val parameter = script.parameters.find { it.name == parameterName } ?: return null
         return analysisSession.firSymbolBuilder.variableLikeBuilder.buildLocalVariableSymbol(parameter.symbol)
     }