Add a new default option to the CDN UI: "all files except CSS+JS", and make this the new default of the CDN module, include upgrade path

This is the PoC patch from #2811615-7: [upstream] [Core bug, fixed since 9.5] AJAX commands that need additional JS to be loaded will fail when JS is loaded from CDN.

#2 was just cosmetic changes; it did not yet have any effect. Now it does.

And now with an upgrade path, plus test coverage.

Self-review.

1. +++ b/cdn.install
   @@ -0,0 +1,31 @@
   + * Install and update functions for the CDN module.
   

   s/Install and update/Update/

2. +++ b/cdn.install
   @@ -0,0 +1,31 @@
   + * Update the default configuration if it's not modified.
   

   s/configuration/settings/

3. +++ b/cdn.module
   @@ -19,7 +19,7 @@ function cdn_help($route_name, RouteMatchInterface $route_match) {
   -        $output .= '<dd>' . t('By letting a CDN serve files instead of your webserver(s), it is possible to significantly reduce the load on your server load and its costs. Note that it may just as well end up costing more — it depends on pricing of the CDN and your server(s).') . '</dd>';
   +        $output .= '<dd>' . t('By letting a CDN serve files instead of your webserver(s), it is possible to significantly reduce the load on your server and its costs. Note that it may just as well end up costing more — it depends on pricing of the CDN and your server(s).') . '</dd>';
   

   IDK how this snuck in here. Unrleated change.

4. +++ b/cdn_ui/src/Form/CdnSettingsForm.php
   @@ -164,9 +165,17 @@ class CdnSettingsForm extends ConfigFormBase {
   +      // Plus one particular common preset: 'media files', which means all files
   

   Outdated, should now say 'nocssjs'.

5. +++ b/src/CdnSettings.php
   @@ -117,7 +126,10 @@ class CdnSettings {
   +        assert(!empty($nested_mapping['conditions']), 'The nested mapping ' . $i . ' includes no conditions, which is not allowed for complex mappings.');
   

   This is validation that should have already existed. Should be done in a separate issue.

6. +++ b/src/CdnSettings.php
   @@ -117,7 +126,10 @@ class CdnSettings {
   +        assert(!empty($nested_mapping['conditions']), 'The nested mapping ' . $i . ' includes no conditions, which is not allowed for complex mappings.');
   +        assert(!isset($nested_mapping['conditions']['not']), 'The nested mapping ' . $i . ' includes blacklist conditions, which is not allowed for complex mappings: the fallback_domain already serves this purpose.');
   

   Both of these should put the assertion logic in single quotes.

7. +++ b/tests/src/Unit/CdnSettingsTest.php
   @@ -25,7 +25,7 @@ class CdnSettingsTest extends UnitTestCase {
   -      'simple, no conditions' => [
   +      'simple, on, no conditions' => [
   
   @@ -37,7 +37,7 @@ class CdnSettingsTest extends UnitTestCase {
   -      'simple, oone empty condition' => [
   +      'simple, on, one empty condition' => [
   
   @@ -69,7 +69,27 @@ class CdnSettingsTest extends UnitTestCase {
   -      'auto-balanced, on, no fallback' => [
   ...
   +      'auto-balanced, on' => [
   

   Out of scope, should be fixed in a separate issue.

8. +++ b/tests/src/Unit/CdnSettingsTest.php
   @@ -198,6 +218,81 @@ class CdnSettingsTest extends UnitTestCase {
   +  /**
   +   * @covers ::getLookupTable
   +   * @expectedException \AssertionError
   +   * @expectedExceptionMessage The nested mapping 0 includes no conditions, which is not allowed for complex mappings.
   +   */
   +  public function testComplexMappingWithoutConditions() {
   +    $this->createCdnSettings([
   +      'status' => TRUE,
   +      'mapping' => [
   +        'type' => 'complex',
   +        'fallback_domain' => 'cdn.example.com',
   +        'domains' => [
   +          0 => [
   +            'type' => 'simple',
   +            'domain' => 'foo.example.com',
   +          ],
   +        ],
   +      ],
   +    ])->getLookupTable();
   +  }
   

   Again out of scope.

9. +++ b/tests/src/Unit/CdnSettingsTest.php
   @@ -198,6 +218,81 @@ class CdnSettingsTest extends UnitTestCase {
   +  public function testComplexDomainWithBlacklist() {
   

   "blacklist" should be replaced with "negative conditions" everywhere?

Addressed everything in #5, except the removal of out-of-scope changes. Opened #2828150: Clean-up + one piece of missing validation for that, and now getting that committed first.

#2828150: Clean-up + one piece of missing validation landed. Rebased.

+++ b/tests/fixtures/update/drupal-8.cdn-cdn_update_8001.php
@@ -0,0 +1,58 @@
+// Install the rest configuration.

s/rest configuration/default CDN settings/

Fixed.

I think this is ready. Thanks, Aurelien, for your feedback! It's much appreciated :) And it helps convince me that this is the right call.

Giving issue credit to Aurelien.