Button: Making all MenuButton props optional

[khmakoto]

Pull request checklist

• Addresses an existing issue: Fixes #0000
• Include a change request file using $ npm run change

Description of changes

This PR makes all of MenuButton props optional so that they don't have to be necessarily provided by the users of the component. This change was spurred by this comment in #8754.

Focus areas to test

(optional)

Microsoft Reviewers: Open in CodeFlow

[JasonGore]

This feels like it would have required some code changes.. I wonder if onMenuDismiss from user props is working. We should verify and add some unit tests as part of this PR to confirm. (Also, will probably break #8931 which is good.)

[msft-github-bot]

Component perf results:

Scenario	Target branch avg total (ms)	PR avg total (ms)	Target branch avg per item (ms)	PR avg per item (ms)
PrimaryButton	103.329	98.555	1.033	0.986
BaseButton	38.447	38.486	0.385	0.385
NewButton	120.598	138.728	1.206	1.387
button	6.057	5.896	0.061	0.059
DetailsRows without styles	203.707	199.361	2.037	1.994
DetailsRows	218.637	218.413	2.186	2.184
Toggles	53.279	53.556	0.533	0.536
NewToggle	70.906	70.177	0.709	0.702
DocumentCardTitle with truncation	27.812	...	0.278	...

[msft-github-bot]

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[khmakoto]

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[msft-github-bot]

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