Improve the names of a few commonly used APIs (#2014)

Motivation:

Naming is important; it should be clear and concise.

Modifications:

The follow renames all offer more precise names:
- Rename `server.run()` to `server.serve()`
- Rename `server.stopListening()` to `server.beginGracefulShutdown()`
- Rename `client.close()` to `client.beginGracefulShutdown()`

Result:

Clearer APIs

Author: glbrntt

Tests/InProcessInteroperabilityTests/InProcessInteroperabilityTests.swift

@@ -29,7 +29,7 @@ final class InProcessInteroperabilityTests: XCTestCase {
       try await withThrowingTaskGroup(of: Void.self) { group in
         group.addTask {
           let server = GRPCServer(transport: inProcess.server, services: [TestService()])
-          try await server.run()
+          try await server.serve()
         }
 
         group.addTask {

Tests/Services/HealthTests/HealthTests.swift

@@ -31,7 +31,7 @@ final class HealthTests: XCTestCase {
 
     try await withThrowingDiscardingTaskGroup { group in
       group.addTask {
-        try await server.run()
+        try await server.serve()
       }
 
       group.addTask {