Explicitly configure wix properties not defaulted from metadata

[pnehrer]

In spite of what the documentation claims, cargo wix doesn't use certain properties defined in the package's [package.metadata.wix] section:

• description
• manufacturer
• product-name
• url

This PR explicitly reads these properties from metadata and populates builder with any values it finds.

[mistydemeo]

Sorry for the late review. Makes sense to me - I'll look into adding this to the tests so we can be sure it works.

[mistydemeo]

In testing now, we are bringing these values in from Cargo.toml. For example, in the axolotlsay test, we're getting the axolotlsay package's description and URL. Is your goal here to override those values with something else?

[pnehrer]

Yes, we were hoping to be able to override these explicitly.