Update all TemplateParts to Match Convention

[robloo]

Describe the bug

Certain controls do not properly name their template parts. These should be renamed to follow convention before the 11.0 release as it is a breaking change for the styles.

This is the breaking-change following PR #7911 and #7994.

Also discussed in #7432

I will also close this one, just adding to keep track of it.

Expected behavior

All template parts should start with the "PART_" prefix as is done in WPF and most controls.

Screenshots

N/A

Desktop (please complete the following information):

• OS: [e.g. Windows, Mac, Linux (State distribution)]
• Version [e.g. 0.10.0-rc1 or 0.9.12]

Additional context
Add any other context about the problem here.

[robloo]

@Takoooooo @maxkatz6

I'm waiting on the big styling updates branch to be merged before I do this. However, it still needs to be done before 11.0. If you want, just let me know a good time to open a PR and I can do this quickly.

[maxkatz6]

Yes, it should be done after control theme changes, otherwise huge conflicts are unavoidable.
Also, not really necessary to have this done in first preview versions.

[robloo]

Now that all the control theme updates are made, I'm going to go through and update template parts within the next week or so.

[robloo]

Adding link to a specific discussion: #3538 (comment)

[robloo]

Well, I had no visibility on the Preview 1 release date or I would have got this in. However, there is a draft PR now.