Use GitInfo to generate the Version Info.

So lets' use the [GitInfo](https://github.com/devlooped/GitInfo) NuGet
Package to generate the required version information for the assemblies
in this repo.
The base version is controlled from `GitInfo.txt`. This is where the
version should be edited.
The NuGet keeps track of the number of commits made since the `GitInfo.txt`
was changed. So unless there is a major version change
(or you run out of numbers) there should be no need to alter the version
on a regular basis.

All of the projects in the repo will then pick up the same version
information was we will set the MSBuild `Version` property as well as
the `InformationalVersion`. The latter will contain the git commit and
branch.

Author: dellis1972

Directory.Build.targets

@@ -0,0 +1,16 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <PackageReference Include="GitInfo" Version="2.1.2" PrivateAssets="all" />
+  </ItemGroup>
+  <PropertyGroup>
+    <GitThisAssembly>false</GitThisAssembly>
+    <GitDefaultBranch>main</GitDefaultBranch>
+  </PropertyGroup>
+
+  <Target Name="SetVersion" BeforeTargets="GetAssemblyVersion;GetPackageVersion" DependsOnTargets="GitVersion">
+    <PropertyGroup>
+      <Version>$(GitSemVerMajor).$(GitSemVerMinor).$(GitSemVerPatch)</Version>
+      <InformationalVersion>$(Version); git-head: $(GitCommit) git-branch: $(GitBranch)</InformationalVersion>
+    </PropertyGroup>
+  </Target>
+</Project>

GitInfo.txt

@@ -0,0 +1 @@
+1.0.0