Unification build Properties

A pull request for this has already been merged.

• #889 by @DocSvartz — merged

@DocSvartz @andrerav Seeing all the repeating of Properties here I would like to suggest to:
- use `Directory.Packages.props` -> introduce CPM

- only one place we need to update
- Configurable along with the Variables of `Directory.Build.props` if you want to ensure to use specific versions of packages for projects like Source Generators or Test Projects (which by the way are missing the common `IsTestProject` Tag, which I added as suggestion to this PR directly)

- use `Directory.Build.props`
- Define NuGet Package Information Centrally - e.g. I found this here and copied it to [my own Repo + adjusted the Properties (Name, License etc.)](https://github.com/DevTKSS/DevTKSS.MyManufacturerERP/blob/d7fbc0f5aef82f526dd7e1e17a5f73dd4ee33d42/Directory.Build.props) I dont use it by now, so adding some other references:
- [First Example](https://github.com/unoplatform/uno.extensions/blob/main/src/Directory.Build.props)
- [Second Example](https://github.com/unoplatform/uno/blob/master/Directory.Build.props)

- source regular Project Props we need repentantly using Variables for example:
- `Directory.Build.props`

```xml


enable
enable
true
net10.0;net9.0;net8.0
Some Name;Some OtherName


```
- Regular `*.csproj`

```xml


$(DefaultTargetFrameworks)
Mapster
Mapster
$(Authors)
Library


```

- Update the Authors Entries?

Never seen those Names recently and @andrerav mentioned in the discussion, he is the only Maintainer except from @DocSvartz and @stagep (potentially missed one 😄 but you get what I mean hopefully) which I did not see in one of those Lists.

_Originally posted by @DevTKSS in https://github.com/MapsterMapper/Mapster/issues/841#issuecomment-3694104162_

Start by reviewing the existing project files together with Directory.Build.props and Directory.Packages.props to identify repeated package, property, and author declarations. Compare the regular *.csproj files and test or source-generator projects against the proposed centralization. Done would mean the agreed properties and package versions are centralized consistently, with project-specific settings preserved; the scope should be confirmed because a related pull request was already merged.

Written by the indexing model from the issue text.