CesiumCurl dependency on libcurl doesn't enable key features like HTTP2

The vcpkg [curl port](https://vcpkg.io/en/package/curl.html) has non-default features for lots of pretty important stuff, like support for HTTP2. That means our default build of CesiumCurl doesn't support HTTP2, which is pretty important for our use-cases. We should go through the list of features and decide which ones we want to enable.

Start by locating CesiumCurl's vcpkg dependency configuration and comparing it with the vcpkg curl port's optional feature list, especially HTTP2 support. Determine which features fit Cesium-native's use cases, then verify that the selected defaults are enabled and that the resulting CesiumCurl build provides the intended capabilities.

Written by the indexing model from the issue text.