feat(@angular/cli): deprecate --prod command line argument

With this change we deprecated the `--prod` command line argument. This argument is confusing especially to new users, since users expect that this builds an application in production mode. This however, is only an alias for `--configuration="production"`

Author: alan-agius4

packages/angular/cli/commands/build-long.md

@@ -3,7 +3,7 @@ When used to build a library, a different builder is invoked, and only the `ts-c
 All other options apply only to building applications.
 
 The application builder uses the [webpack](https://webpack.js.org/) build tool, with default configuration options specified in the workspace configuration file (`angular.json`) or with a named alternative configuration.
-A "production" configuration is created by default when you use the CLI to create the project, and you can use that configuration by specifying the `--configuration="production"` or the `--prod` option.
+A "development" configuration is created by default when you use the CLI to create the project, and you can use that configuration by specifying the `--configuration development`.
 
 The configuration options generally correspond to the command options.
 You can override individual configuration defaults by specifying the corresponding options on the command line.

packages/angular/cli/commands/definitions.json

@@ -22,7 +22,8 @@
         },
         "prod": {
           "description": "Shorthand for \"--configuration=production\".\nSet the build configuration to the production target.\nBy default, the production target is set up in the workspace configuration such that all builds make use of bundling, limited tree-shaking, and also limited dead code elimination.",
-          "type": "boolean"
+          "type": "boolean",
+          "x-deprecated": "Use `--configuration production` instead."
         }
       }
     },

packages/angular/cli/models/architect-command.ts

@@ -328,6 +328,7 @@ export abstract class ArchitectCommand<
       if (commandOptions.prod) {
         // The --prod flag will always be the first configuration, available to be overwritten
         // by following configurations.
+        this.logger.warn('Option "--prod" is deprecated: Use "--configuration production" instead.');
         configuration = 'production';
       }
       if (commandOptions.configuration) {