In a nutshell, when we understand that the expression is a function
call (this happens at '(' after an expression), stop parsing expression
and start parsing function arguments. This makes
`FunctionCallCanonicalizationPass` and the workaround for zero argument
function calls obsolete.
We cannot handle them normally since we need text between parenthesis to
be a valid expression. As a workaround, we now push an artificial value
to stack to act as an argument (it'll be later removed during function
call canonicalization).
This commit introduces NamedVariableDeclaration and
SSAVariableDeclaration and allows storing both of them in Variable node.
Also, it adds additional structures in FunctionDefinition and
BasicBlock, which will be used to store SSA form related information.
This class stores a non-owning raw pointer to a member of `Node`, so
extra care is needed to ensure that referenced `Node`s will be alive
by the time `NodeSubtreePointer` is used. Since we only need to use this
class while traversing AST in `RecursiveASTVisitor`, access to class
methods can be restricted using `Badge<RecursiveASTVisitor>`.
Currently, they are not extremely useful, but the plan is to store
all function-local state in JSSpecCompiler::Function and all
"translation unit" state in ExecutionContext.
