Handle errors gracefully if Provider does not implement functions

[friedger]

Currently, Xverse does not support profileUpdateRequest

Developers need to manually check for feature like this

    const provider = getStacksProvider();
    if (provider.profileUpdateRequest) {
...

[janniks]

connect could check before calling a function. Right now we only have onCancel which could be used, or throw an error (not sure how graceful that is)