Unnecessary escaping in logs returned from secret contracts

[reuvenpo]

@baedrik noticed an issue when trying to pass characters that are usually escaped in strings, through secret contract logs.

The flow here is:

• Pass a string to the cosmwasm_std::log function
• Return it from the handle/query/init function
• Read it with secretcli q compute tx

He observed that e.g. a literal " turns into a literal \\\", and \n (a newline) turned into a literal \\n

This is probably a compound of two different serialization bugs in different parts of the system, because of the double escaping.

EDIT: marked as "good first issue" since it's probably a simple programming error, and could get someone new familiar with the codebase, if they want to start contributing.