Add inlineProjections, an AST rewriter that inlines projections where possible

o Also make sure that the AST only contains AliasedReturnItems when planning
o Remove WITH * when building Query Graph
o Removed commands.ReturnItem.renamed
o Removed inlineNamedPaths (replaced by inlineProjections)
o Fix OptionalExpandPipe to emit nulls when given a null identifier
o Introduce AstConstructionTestSupport
o Introduce IsAggregate, containsAggregate