Missing `|` and `&` from syntax highlighting

[scotttrinh]

These characters are parsed as just source.edgeql instead of keyword.operator.edgeql and source.edgeql.

[aljazerzen]

The problem is that:

• we generate this grammar from introspecting the schema,
• operators are generated from schema::Operator,
• | and & are not operators, since they are used in type expressions.

We should add a way to mark tokens other than actual operators as operators.