[<InlineIfLambda>] Usage

[delneg]

Hello,

I've thought that maybe this project can benefit from usage of InlineIfLambda attribute, however I'm not sure if it will break the compatibility with users on non-net6 runtimes.
Should it be considered using the current targets or is it not backwards-compatible ?
Also, there could be other things we might use from the latest FSharp.Core

[dsyme]

IIL can be used targeting any framework, as long as you're compiling with F# 6