fix: reverse showSaveDialog cancellation bool

[codebytere]

Description of Change

Addresses the issue raised in this comment.

The cancellation boolean values were reversed, in that ShowSaveDialogSync returned true if the dialog was not cancelled and we were unilaterally passing it to the completion callback as the canceled value. We also should be returning canceled as true if CreateDialogThread returned false.

This PR thus corrects that error.

cc @miniak

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Corrected a reversal of cancellation values in showSaveDialog on the Windows platform.

[release-clerk]

Release Notes Persisted

Corrected a reversal of cancellation values in showSaveDialog on the Windows platform.

[trop]

I have automatically backported this PR to "6-0-x", please check out #18383