Make computed properties reactive to document.web3network changes

[mds1]

Problem

The list of supported zkSync tokens is stored as a computed property called zkSyncSupportedTokens. It's dependent on document.web3network. Vue cannot react to changes in document, so when the network changed this was not updated.

This means if a user visits the cart, then connects their wallet, the network change would not be detected, and zkSyncSupportedTokens would return an empty list. As a result, they would not be able to checkout with zkSync.

Solution

We fix this by adding a new property to the component. Vue can watch and react to changes in this new property, and we update this new property when the dataWalletReady event is detected. We also make the mainnet token list the default when nothing is detected

cc @octavioamu @thelostone-mc

[mds1]

I also added a commit to add SNT support here since that was recently added by zkSync