ES2021 Logical Assignment

[ljqx]

Steps to reproduce

esprima.parse('a ||= b;')

Expected output

A syntax tree.

Actual output

Error: Line 1: Unexpected token =

Relevant references

Proposal: https://github.com/tc39/proposal-logical-assignment
ESTree: https://github.com/estree/estree/blob/master/es2021.md#assignmentoperator

[Meir017]

@ariya @ljqx I think this can be closed now