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add spelling checking script
**What this PR does / why we need it**:
Add spell checking script to avoid involving any typos.
Currently many small PRs are fixing those annoying typos, which is time-consuming and low efficient. We should add such a preflight check before a PR gets merged.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
/sig testing
/area test-infra
/sig release
/cc @ixdy
/assign @liggitt @smarterclayton
**Release note**:
```release-note
add spelling checking script
```
ec77ddfe19