The schema is in https://core.telegram.org/schema/json so it's more
logical to expect the file to be named `json`, which is what would
happen if you download it with wget, for example.
Because we might use dependencies soon that require this framework.
And anyway these days the .NET world is mostly a hybrid between
.NETStandard/.NETCore libs and .NET4.6 ones, not older than that.
(This commit was brought from TLSharp [1] version 0.1.0.522.)
[1] 709e5be7cc