Adding polling restart for TokenList Fetch

[NiranjanaBinoy]

To make sure the TokenList id fetched from the API only when there is a change in chainId or UsestaticTokenList flag specifically and clear all previous polling interval schedules before scheduling a polling interval.

[danjm]

This looks good. I only have one nitpick: given the name startPolling feels slightly misleading if we are going to stop and the beginning of the call.

Suggestion: create a method called restart :

async start() {
    this.stopPolling();
    await this.startPolling();
  }

Then call this in the network and preference change handlers. And also remove the the stop call in startPolling

[danjm]

LGTM