api_proto_plugin: Normalize `SourceCodeInfo.comments` in `type_context` (#22025)

This is a general cleanup to shift responsibility for normalizing comment strings in type_context

This will make it easier to shift protodoc to templates, and also will enforce comments have a preceding space - ie // comment not //comment and prevent bugs as can be seen here https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/network/sip_proxy/v3alpha/sip_proxy.proto.html?highlight=sip_proxy#extensions-filters-network-sip-proxy-v3alpha-localservice

it also shifts some v inefficient closures

Signed-off-by: Ryan Northey <ryan@synca.io>

Mirrored from https://github.com/envoyproxy/envoy @ 73e0ccf945975fc913847a1f2792ba3e1277a8c0

contrib/envoy/extensions/filters/network/sip_proxy/v3alpha/sip_proxy.proto

@@ -153,9 +153,9 @@ message Cache {
 
 // Local Service
 message LocalService {
-  //The domain need to matched
+  // The domain need to matched
   string domain = 1;
 
-  //The parameter to get domain
+  // The parameter to get domain
   string parameter = 2;
 }