Single-file Publish

Single-file Publish is required to be presented for functions in order to improve loading and cold-starts **right-now**

Moreover, new improvements are going to be provided with the upcoming .NET 5 should be taken into account: [URL](https://github.com/dotnet/designs/blob/98c7ac94077a81dd78c6de24c4f60fed380a1dfe/accepted/2020/single-file/design.md
)

Start by reading the linked .NET 5 single-file design document and the issue's requirement for Azure Functions. Identify the host entry points involved in publishing functions and determine how the proposed improvements apply. Done means establishing a concrete implementation scope for single-file publishing and validating its effect on loading and cold starts.

Written by the indexing model from the issue text.