Refactor DetermineTargetFramework to use msbuild & support multiple tfms

[liliankasem]

Issue describing the changes in this PR

resolves #4670

Pull request checklist

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Additional information

Additional PR information

[mattchenderson]

Approving for CI testing, but not to merge.

[jviau]

Probably work for a different PR, if at all. Determining TFM from core tools doesn't work when the function app is multi-targeted. This change is definitely an improvement, but it will have the same multi-target issue.

Is there a framework parameter for func cli? Should we add one? Or consider this area not supported and error out when TFM cannot be found?

Using dotnet run target does work here, as you can specify the TFM for it.

[liliankasem]

Probably work for a different PR, if at all. Determining TFM from core tools doesn't work when the function app is multi-targeted. This change is definitely an improvement, but it will have the same multi-target issue.

Yeah I think support for multiple TFMs is a little rough at the moment. I can definitely add a check for TargetFrameworks and prompt the user for which of the TFMs they would like to use from that list.

The determine TFM method comes into play for something like --docker-only where you have already initialized the worker with a TFM i.e.

func init --worker-runtime dotnet-isolated --target-framework net10.0

But now you're like "I want docker too!"

func init --docker-only

In which case we will a) determine worker from local settings and b) determine tfm via this method

We could also add support for func init --docker-only --target-framework net10.0 but I don't want to break the scenario where you just do the docker param.

Is there a framework parameter for func cli? Should we add one? Or consider this area not supported and error out when TFM cannot be found?

Yeah there is already a tfm param for func init

--target-framework Initialize a project with the given target framework moniker. Currently supported only when --worker-runtime set to dotnet-isolated or dotnet. Options are - net10.0, net9.0, net8.0, net7.0, net6.0, net48