Don't compile widgets on tvOS and watchOS by default

Widgets is not particularly useful on tvOS without significant work due
to the focus model, and widgets is completely useless on watchOS except,
theoretically, a platform plugin which displays its UI over the network.

Widgets is not particularly nice on iOS either but is at least usable so
it remains enabled there.

This is sort of a revert of b4ebb61c0d,
except that this now simply turns off the feature by default rather than
disabling its use entirely.

Change-Id: Ice4215c344da4568792f8b5356e11367bde6828f
Reviewed-by: Mike Krus <mike.krus@kdab.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

configure.json

@@ -2120,6 +2120,7 @@
         },
         "widgets": {
             "description": "Qt Widgets",
+            "autoDetect": "!config.tvos && !config.watchos",
             "condition": "features.gui",
             "output": [
                 "privateFeature",