Issue #3155258 by jwilson3, alexpott, lauriii: Use American English spelling of "gray"

core/.cspell.json

core/misc/cspell/dictionary.txt

core/misc/dialog/off-canvas.reset.css

core/modules/media/tests/fixtures/oembed/rich_twitter.json

...odules/media/tests/fixtures/oembed/video_collegehumor.xml

...les/media/tests/fixtures/oembed/video_vimeo-no-title.json

core/modules/media/tests/fixtures/oembed/video_vimeo.json

core/modules/media/tests/fixtures/oembed/video_youtube.json

...s/src/FunctionalJavascript/MediaSourceOEmbedVideoTest.php

core/modules/settings_tray/css/settings_tray.theme.css

core/modules/shortcut/shortcut.module

core/themes/claro/css/base/elements.css

core/themes/claro/css/base/off-canvas.theme.css

core/themes/claro/css/base/variables.css

core/themes/claro/css/base/variables.pcss.css

core/themes/claro/css/components/accordion.css

core/themes/claro/css/components/action-link.css

core/themes/claro/css/components/action-link.pcss.css

core/themes/claro/css/components/ajax-progress.module.css

...emes/claro/css/components/autocomplete-loading.module.css