Improve build-all.ps1 script

[jordimontana82]

In order to making the cloning and building of all the different repos and packages a bit more seamless, the build script could be improved to:

• [ ] Show a warning if you're not in a DynamicsValue parent folder: to highlight the fact repos should have the same parent folder
• [ ] Prompt any warnings if some of the target frameworks or SDKs are missing
• [ ] Check if the local-packages folder exist, otherwise create it, via confirm
• [ ] Check if a folder for each repo exists, otherwise git clone it, via confirm
• [ ] Run git-pull.ps1 on all repos after they've been downloaded
• [ ] Build & publish everything into local-packages

[BetimBeja]

+ we should add an easy way to distinguish v2 from the latest v3 😄 maybe different scripts would be easier for the first-time users

[jordimontana82]

I wanted to keep the same scripts for both versions though, to keep it simple (or less complex than it is :P) it's the branch that will define if you're building 2x or 3x. Maybe an info message at the end to highlight if you're in one version or another?

Although one can see it from VS Code or VS....