Add Symfony's Filesystem and Finder components to core

Looks good except for one out of scope change to the root composer.json.

I think the nightwatch failures are unrelated to these changes. In the Nightwatch job at Tests/Olivero/oliveroColorTest.js:

unhandledRejection: stale element reference: element is not attached to    ││   the page document 

Believe it needs a manual rebase. Says it's unmergable .

Latest reroll looks good to me.

Discussed at length at Drupalcon with @catch we agreed to add these as full runtime dependencies to make generating themes simpler and because they are there if you require Drush.

Committed 7f540d8 and pushed to 11.x. Thanks!

leaving open for backport to 10.2.x

alexpott → credited catch → .

Discussed with @catch and we agreed to backport.

Automatically closed - issue fixed for 2 weeks with no activity.