[packages] Make package !include vars visible to its substitutions block (#16274)

tests/unit_tests/fixtures/substitutions/18-package_vars_in_subs.approved.yaml

@@ -0,0 +1,9 @@
+binary_sensor:
+  - platform: template
+    id: front_door_enrolling
+    name: Front Door Enrolling
+substitutions:
+  enrolling_id: front_door_enrolling
+  enrolling_name: Front Door Enrolling
+esphome:
+  name: test

tests/unit_tests/fixtures/substitutions/18-package_vars_in_subs.input.yaml

@@ -0,0 +1,9 @@
+esphome:
+  name: test
+
+packages:
+  fingerprint: !include
+    file: 18-package_vars_in_subs_inc.yaml
+    vars:
+      sensor_name: "Front Door"
+      sensor_id_prefix: "front_door"

tests/unit_tests/fixtures/substitutions/18-package_vars_in_subs_inc.yaml

@@ -0,0 +1,8 @@
+substitutions:
+  enrolling_id: ${sensor_id_prefix}_enrolling
+  enrolling_name: ${sensor_name} Enrolling
+
+binary_sensor:
+  - platform: template
+    id: ${enrolling_id}
+    name: ${enrolling_name}