Accessibility Insights warnings: tab stops and bounds fix.

[johnbeisner]

More Accessibility Insights fixes.

Reference: dotnet/core-setup#5549
Related: #1012

/cc @merriemcgaw @joeloff @dleeapho @dagood

[livarcocc]

@merriemcgaw gave me a list of other interesting scenarios to try. @johnbeisner could you try it out: Keyboard accessiblity (can you use the installer without a mouse) / High Contrast / Magnifier

[johnbeisner]

Keyboard accessiblity - good experience
High Contrast # 1 - good experience
High Contrast # 2 - good experience
High Contrast Black - the hyperlinks are hard to read
High Contrast White - good experience
Magnifier - good experience

[KathleenDollard]

Is this us or MSI?

[merriemcgaw]

This is not a standard MSI window, we or WiX must be setting it.

[johnbeisner]

The colors for the text, banner, background, et al are defined in the theme:
https://github.com/dotnet/core-sdk/blob/edadf5a7c504a551a0c2adee6df604e7263b303d/src/redist/targets/packaging/windows/clisdk/bundle.thm#L4-L9

The frame, buttons, links are defined by the 'High Contrast'

[johnbeisner]

@merriemcgaw
Opened: #1130