Add the Symbolic Binding Operator ("as") to the operator priority table

[asharpe]

Describe the bug
The "as" operator is missing from the operator priority table

To Reproduce
Visit https://github.com/jqlang/jq/wiki/jq-Language-Description#operators-priority

Expected behavior
The "as" operator appears in the table

Environment (please complete the following information):
n/a

[itchyny]

Currently the precedence of as is higher than the unary operator -, but I'm thinking of change it between the unary operator and multiplication operators, see #3053.