@Override
    protected boolean isMapKey() {
        return isLhs();
    }
A map parsing context. Just a PairContext that responds to isMapKey
depending on whether or not we're parsing the left hand side of a
key/value pair.

@author Alex Roetter
thrift/thrift0.13/src/main/java/com/linecorp/armeria/common/thrift/text/MapContext.java