Add property of AudioContext state API

[rixrix]

Hi

This fixes microsoft/TypeScript#5816

This is my first PR, would be good if someone can give feedback. thanks

[msftclas]

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[msftclas]

@rixrix, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

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[mhegazy]

the webidl files are not supposed to change. please see https://github.com/Microsoft/TSJS-lib-generator#contribution-guide for how you can augment definitions.

[rixrix]

@mhegazy great, I'll look into it. thanks

[rixrix]

@mhegazy if you could look at it again, that'd be great. Previous change set was definitely a mistake. cheers

[mhegazy]

👍

[zhengbli]

👍 Thanks for the contribution @rixrix !