This adds the `static` token to the lexer and parses it as a modifier.
In check, `FullPatternStack::Kind::FieldDecl` is now used for both
static and non-static vars. Static vars get treated basically the same
as `NameBindingDecl`s.
Global initialization is used for static var initializers. To make the
necessary stack information available to `pattern_match.cpp`, the
`full_pattern_stack` and `decl_introducer_state_stack` are now popped
later in `handle_let_and_var.cpp`.
In lowering, each class's body is checked for `VarStorage` insts and
lowered the same as global vars.
Creates a `GlobalInit` class for storing relevant values, pulling
functions off `InstBlockStack` and `Context`. Adds a `Context` pointer
just so that it doesn't need to be passed in on each call (`Finalize` in
particular uses several members).
Note we have several different `InstBlockStack` instances, so several
copies of the relevant members were simply unused.
Nicholas Bishop
Jon Ross-Perkins