Use @soroban-react/contracts library

[esteblock]

Move useContractValue and useSendTransaction functions to @soroban-react/contracts library
This will make soroban's dapps development easier.

Now supporting useContractValue function

[paulbellamy]

Overall looks good. I added a few code styling fixups. I like the more explicit named parameters to useContractValue. More extensible, and clearer what you're doing.

I opened paltalabs/soroban-react#5. With that, I think we can remove all the places we pass sorobanContext to useContractValue, and let it use the default. That should make useContractValue easier to use for users as well.

[esteblock]

@paulbellamy
I added #80 changes into @soroban-react/contracts library in paltalabs/soroban-react#16
Then manually merged #80 with #79.
Also tried. Works ok :)

It's just failing in Rust / build-and-test (ubuntu-latest, x86_64-unknown-linux-gnu, true) (pull_request)
But it's the same error #80 has.

[paulbellamy]

Looks great, thanks so much!