[js/rn] Fix some bugs (#20242)
### Description
<!-- Describe your changes. -->
- Fix `logSeverityLevel`
- Correct get RCTCxxBridge, old method for some cases will got wrong
bridge
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
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Co-authored-by: Yulong Wang <7679871+fs-eire@users.noreply.github.com>
