Fix global.json latestPatch roll-forward parsing

[runesoerensen]

We currently treat patch/latestPatch and feature/latestFeature roll-forward policies equally.

However, the latestPatch/patch policy should define a version requirement that only allow values in a specific "feature band" (e.g. allows 8.0.102 or any later 8.0.1xx version, such as 8.0.103 or 8.0.199, but not 8.0.403)).

The .NET SDK doesn't technically follow semantic versioning (more details here), but treating it as such (using the semver crate) is adequate for most scenarios. It seems unlikely that users will even want to specify latchPatch rather than latestFeature, but this is one edge case that we may want to account for in our version parsing logic.

Currently, the buildpack will install a more recent SDK than expected when the latestPatch roll-forward policy is defined (and a more recent "feature band" release is available), and dotnet publish will throw an error as a result.