Implement binding of the values in dotty.tools.repl.ReplDriver.bind

[SzymonPajzert]

#4933 currently uses stub to perform value binding during initialization commands. After it is merged, actual binding should be performed.

This issue is a follow up to #3007

[IDoCodingStuffs]

@allanrenucci can take this one on if help is still needed

[allanrenucci]

Sure! Help very much appreciated!