Generate code using fully qualified type names

[dmytr]

Currently code generator produces code that uses fully qualified type names conditionally. This can cause shadowing of packages by local identifiers.

This is somewhat related to #1911, but there are more cases when this problem occurs.

For example:

syntax = "proto3";

package echo;

service EchoService {
  rpc Echo(EchoMessage) returns (EchoMessage);
}

message EchoMessage {
  string echo = 1;
}

Causes the following compilation error:

[error] -- [E046] Cyclic Error: /home/me/example/target/scala-3.3.6/src_managed/main/echo/echo/EchoServiceGrpc.scala:28:22
[error] 28 |    def echo(request: echo.echo.EchoMessage): scala.concurrent.Future[echo.echo.EchoMessage]
[error]    |                      ^
[error]    |                      Cyclic reference involving method echo
[error]    |
[error]    |                       Run with -explain-cyclic for more details.
[error]    |
[error]    | longer explanation available when compiling with `-explain`

This PR changes code generator to always use fully qualified type names, which should prevent majority of cases where shadowing could cause a problem.

[dmytr]

Job build (2_12, examples_and_formatting) was failing because generated code had to be updated. I've run ./examples_and_formatting.sh and committed the resulting changes in Format generated sources.

[dmytr]

Hi @thesamet, maybe you could take a look when you have time, please? 🙏 Only the first commit contains actual changes. The second one contains only changes of generated code. Effective changes are quite small.

[dmytr]

@thesamet thank you for merging this PR. Maybe you could publish it as an alpha3 release as well, please? Once it's published I could take it for a spin in our project. Thanks again!

[thesamet]

Done