getSupportedPlatforms is called multiple times by device selector #3886
Description
While testing #3856 with a folder open that contains a web_only and web_and_ios project, duplicate requests are sent for supported platforms when I click the device in the status bar to open the picker. The log says "Checking 4 projects", but there are only two.
[5:51:29 PM] [General] [Info] Checking 4 projects for supported platforms
[5:51:29 PM] [FlutterDaemon] [Info] ==> [{"id":"29","method":"daemon.getSupportedPlatforms","params":{"projectRoot":"/Users/danny/Desktop/dart_samples/different_platform_projects/web_and_mobile"}}]
[5:51:29 PM] [FlutterDaemon] [Info] ==> [{"id":"30","method":"daemon.getSupportedPlatforms","params":{"projectRoot":"/Users/danny/Desktop/dart_samples/different_platform_projects/web_only"}}]
[5:51:29 PM] [FlutterDaemon] [Info] ==> [{"id":"31","method":"daemon.getSupportedPlatforms","params":{"projectRoot":"/Users/danny/Desktop/dart_samples/different_platform_projects/web_and_mobile"}}]
[5:51:29 PM] [FlutterDaemon] [Info] ==> [{"id":"32","method":"daemon.getSupportedPlatforms","params":{"projectRoot":"/Users/danny/Desktop/dart_samples/different_platform_projects/web_only"}}]
[5:51:29 PM] [FlutterDaemon] [Info] <== [{"id":"29","result":{"platforms":["ios","web"]}}]
[5:51:29 PM] [FlutterDaemon] [Info] <== [{"id":"30","result":{"platforms":["web"]}}]
[5:51:29 PM] [FlutterDaemon] [Info] <== [{"id":"31","result":{"platforms":["ios","web"]}}]
[5:51:29 PM] [FlutterDaemon] [Info] <== [{"id":"32","result":{"platforms":["web"]}}]
[5:51:29 PM] [General] [Info] Supported platforms for the workspace are ios, web