Give more useful error messages when Burn fails to load theme controls

[wixbot]

If there is an issue with a customization of one of the themes in WixStdBA, the error message is simply "Failed to load theme controls." I eventually tracked this down to a missing png file. However, it would have saved me a couple hours' time if the error had said, "Can't find logo,png referenced by 'Image' element on Page 'Install' in theme file 'CustomTheme.thm'. Just more detail to eliminate guesswork! :)

Originally opened by software.mike.johnson

[wixbot]

This is related to issue 4587.

Originally posted by software.mike.johnson

[wixbot]

Needs some infrastructure to support piping all the library messaging through to the BA so it log via Burn.

Area changed from burn to sdk
Release changed from v3.9 to v4.x

[rseanhall]

WixStdBA logs thmutil error messages into the bundle's log in v4.0. ThmViewer has also been updated to show thmutil error messages. For the specific case of a missing png file, #4860 might need to be addressed for a more helpful message.

wixtoolset/Bal.wixext#20
wixtoolset/balutil#11
wixtoolset/balutil#12
wixtoolset/burn#14
wixtoolset/Tools#39
wixtoolset/wcautil#4
wixtoolset/dutil#10