Deny bevy subcrate imports in examples

[alice-i-cecile]

          existing CI is

bevy/.github/workflows/ci.yml

Lines 418 to 438 in 612897b

	check-bevy-internal-imports:
	runs-on: ubuntu-latest
	timeout-minutes: 30
	steps:
	- uses: actions/checkout@v4
	- name: Check for bevy_internal imports
	shell: bash
	run: |
	errors=""
	for file in $(find examples tests -name '*.rs'); do
	if grep -q "use bevy_internal" "$file"; then
	errors+="ERROR: Detected 'use bevy_internal' in $file\n"
	fi
	done
	if [ -n "$errors" ]; then
	echo -e "$errors"
	echo " Avoid importing bevy_internal, it should not be used directly"
	echo " Fix the issue by replacing 'bevy_internal' with 'bevy'"
	echo " Example: 'use bevy::sprite::MaterialMesh2dBundle;' instead of 'bevy_internal::sprite::MaterialMesh2dBundle;'"
	exit 1
	fi

it currently only checks for bevy_internal imports, it could be extended to others

Originally posted by @mockersf in #15317 (comment)

[JMS55]

I very much would like this.