Issue #3474499 by quietone, nicxvan: Fix spelling of 3 'base' words

core/.phpstan-baseline.php

core/includes/theme.inc

core/lib/Drupal/Core/Asset/CssOptimizer.php

core/misc/cspell/dictionary.txt

...ules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php

...odules/config/tests/src/Functional/ConfigImportUITest.php

core/modules/media/src/MediaSourceBase.php

.../entity_test/src/Entity/EntityTestMultiValueBaseField.php

.../modules/system/tests/src/Functional/System/ThemeTest.php

...dules/system/tests/src/Functional/Theme/ThemeInfoTest.php

core/modules/system/tests/src/Kernel/Theme/ThemeTest.php

...test_base_theme/config/install/core.date_format.fancy.yml

...st_base_theme/config/install/test_base_theme.settings.yml

.../test_base_theme/config/schema/test_base_theme.schema.yml

...tem/tests/themes/test_base_theme/test_base_theme.info.yml

...ests/themes/test_base_theme/test_base_theme.libraries.yml

...system/tests/themes/test_base_theme/test_base_theme.theme

.../test_invalid_base_theme/test_invalid_base_theme.info.yml

...valid_base_theme_sub/test_invalid_base_theme_sub.info.yml

...m/tests/themes/test_subsubtheme/test_subsubtheme.info.yml