Legacy DDlog tokens

Sources using the rejected legacy syntax below now produce parser errors and no lint diagnostics from Runner::run. Migrate the syntax before relying on lint results.

The parser keeps legacy token kinds in the lexer so diagnostics can point to the exact source span, but unsupported legacy syntax is rejected during parsing.

• Use type Foo = ... instead of typedef Foo = ....
• Use sized integer types such as i64, u64, and u32 instead of bigint or bit<N>.
• Use f64 instead of double.
• Use f32 instead of float.
• Use signed sized integer types such as i32 instead of signed<N>.
• Remove <=>; it was reserved upstream but has no DDlog semantics in ddlint.
• Use #[...] for attributes. A bare # is rejected.

as remains valid in supported grammar positions, including import aliases such as import foo::bar as baz.