implement BigInt multiplication

Question

This is a follow-up on 76. implement BigInt addition with sign.

You are asked to create a function that multiplies two big integers in string.

multiply(
  '1123456787654323456789', 
  '1234567887654323456'
)
// '1386983673205309924427166592431045142784'

Code

/**
 * @param {string} a 
 * @param {string} b
 * @return {string}
 */
function multiply(a, b) {
  // your code here
}

Source

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