web: use mixin for additional product configuration
web: use mixin for additional product configuration

cc @bpasero

using the ... operator will forcefully override object based configurations, such as `extensionEnabledApiProposals`. we should use mixin instead, since that allows us to recursively mixin properties

microsoft/vscode,eamodio/vscode,eamodio/vscode,eamodio/vscode,eamodio/vscode,microsoft/vscode,eamodio/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,eamodio/vscode,microsoft/vscode,eamodio/vscode,eamodio/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,eamodio/vscode,microsoft/vscode,eamodio/vscode,microsoft/vscode,microsoft/vscode,microsoft/vscode,eamodio/vscode,microsoft/vscode,microsoft/vscode,eamodio/vscode,eamodio/vscode,eamodio/vscode,eamodio/vscode,eamodio/vscode,microsoft/vscode,eamodio/vscode