[build] Suppress NuGet warnings (#730)

Suppress some NuGet warnings:
* `logcat-parse.csproj`
Warning NU1701: Package 'Mono.CSharp 4.0.0.143' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8' instead of the project target framework '.NETCoreApp,Version=v3.1'. This package may not be fully compatible with your project.
* `Java.Interop.csproj`
Warning NU1702: ProjectReference 'D:\…\build-tools\jnienv-gen\jnienv-gen.csproj' was resolved using '.NETFramework,Version=v4.7.2' instead of the project target framework '.NETStandard,Version=v2.0'. This project may not be fully compatible with your project.

Author: jpobst

src/Java.Interop/Java.Interop.csproj

@@ -15,6 +15,7 @@
  <LangVersion>8.0</LangVersion>
  <Nullable>enable</Nullable>
  <ProduceReferenceAssembly>true</ProduceReferenceAssembly>
+ <MSBuildWarningsAsMessages>NU1702</MSBuildWarningsAsMessages>
  </PropertyGroup>
  <PropertyGroupCondition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
  <DefineConstants>DEBUG;$(DefineConstants)</DefineConstants>
@@ -79,4 +80,4 @@
  </Properties>
  </MonoDevelop>
  </ProjectExtensions>
-</Project>
+</Project>

tools/logcat-parse/logcat-parse.csproj

@@ -12,7 +12,7 @@
  <ItemGroup>
  <PackageReferenceInclude="Mono.Options"Version="5.3.0.1" />
  <PackageReferenceInclude="Mono.Terminal"Version="5.4.0" />
- <PackageReferenceInclude="Mono.CSharp"Version="4.0.0.143" />
+ <PackageReferenceInclude="Mono.CSharp"Version="4.0.0.143"NoWarn="NU1701"/>
  <PackageReferenceInclude="Microsoft.NETFramework.ReferenceAssemblies"PrivateAssets="All"Version="1.0.0" />
  </ItemGroup>