feat: implement SplitButton component - #5077

No release type found in pull request title "K0ndee/split button". Add a prefix to indicate what kind of release this pull request corresponds to. For reference, see https://www.conventionalcommits.org/ Available types: - feat: A new feature - fix: A bug fix - docs: Documentation only changes - style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc) - refactor: A code change that neither fixes a bug nor adds a feature - perf: A code change that improves performance - test: Adding missing tests or correcting existing tests - build: Changes that affect the build system or external dependencies (example scopes: gulp, broccoli, npm) - ci: Changes to our CI configuration files and scripts (example scopes: Travis, Circle, BrowserStack, SauceLabs) - chore: Other changes that don't modify src or test files - revert: Reverts a previous commit