[local_auth] The alert should be called in the main thread.

[callbiruk]

This fix resolves:
(NSException *) exception = 0x0000000280f86df0 name: "NSInternalInconsistencyException" - reason: "Modifications to the layout engine must not be performed from a background thread after it has been accessed from the main thread."

Description

This PR resolves an issue for a complete app crash when the biometric lockout happens in the app. The alert throws an error claiming the UI modification should happen in the main thread instead of the background process. Therefore, I run the function in the main thread and wrap it on try catch block for any failure.

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[cyanglaz]

I'm going to close the PR because the CLA is not signed. Feel free to ping me when the CLA is signed and I'll re-open the PR. Or you can open a new PR after signing the CLA.

[callbiruk]

@googlebot I signed it!

I'm going to close the PR because the CLA is not signed. Feel free to ping me when the CLA is signed and I'll re-open the PR. Or you can open a new PR after signing the CLA.

@googlebot I signed it!

[cyanglaz]

@googlebot I fixed it

[callbiruk]

@cyanglaz Request for approval.

[stuartmorgan-g]

Closing as a duplicate of #3352