fix(auth): Setting Store Tokens should only clear tokens that no longer have a value (#13584)

* Setting Store Tokens should only clear tokens that no longer have a value.  This resolves thrashing events when a consumer is listening to storage events, preventing them from seeing a 'clear' followed immediatly by a 'set' value.

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Co-authored-by: AllanZhengYP <zheallan@amazon.com>
Co-authored-by: Joon Choi <13882232+joon-won@users.noreply.github.com>
Co-authored-by: Hui Zhao <10602282+HuiSF@users.noreply.github.com>

Author: 4 people