cmd/tailscale,feature/featuretags: make webbrowser and colorable deps omittable

Add new "webbrowser" and "colorable" feature tags so that the
github.com/toqueteos/webbrowser and mattn/go-colorable packages
can be excluded from minbox builds.

Updates #12614

Change-Id: Iabd38b242f5a56aa10ef2050113785283f4e1fe8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

feature/buildfeatures/feature_colorable_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_colorable
+
+package buildfeatures
+
+// HasColorable is whether the binary was built with support for modular feature "Colorized terminal output".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_colorable" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasColorable = false

feature/buildfeatures/feature_colorable_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_colorable
+
+package buildfeatures
+
+// HasColorable is whether the binary was built with support for modular feature "Colorized terminal output".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_colorable" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasColorable = true

feature/buildfeatures/feature_webbrowser_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_webbrowser
+
+package buildfeatures
+
+// HasWebBrowser is whether the binary was built with support for modular feature "Open URLs in the user's web browser".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_webbrowser" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasWebBrowser = false

feature/buildfeatures/feature_webbrowser_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_webbrowser
+
+package buildfeatures
+
+// HasWebBrowser is whether the binary was built with support for modular feature "Open URLs in the user's web browser".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_webbrowser" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasWebBrowser = true