Merge #16309: [MSVC] allow user level project customization

c83f0ac [MSVC] allow user level project customization (nicolas.dorier)

Pull request description:

  This PR allow the user to customize the build process.

  For example with the following `common.init.vcxproj.user` file
  ```xml
  <?xml version="1.0" encoding="utf-8"?>
  <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <PropertyGroup>
      <CLToolExe>clcache.exe</CLToolExe>
      <CLToolPath>C:\ProgramData\chocolatey\bin\</CLToolPath>
      <TrackFileAccess>false</TrackFileAccess>
    </PropertyGroup>
  </Project>
  ```
  I can use `clcache` while developing in visual studio.

ACKs for top commit:
  sipsorcery:
    tACK c83f0ac.
  fanquake:
    ACK c83f0ac. I did not test the customization.

Tree-SHA512: beef4ac97ed4e1ef46c358629101a008b7df81ca96f3ef7e0947788a6c295c1dddd00a93a09c1aa9daa68a6da0c4ab271aa5dd23df35f3fc8f453ee929e047f8

Author: fanquake

build_msvc/common.init.vcxproj

@@ -115,4 +115,5 @@
       <AdditionalDependencies>crypt32.lib;Iphlpapi.lib;ws2_32.lib;Shlwapi.lib;kernel32.lib;user32.lib;gdi32.lib;winspool.lib;comdlg32.lib;advapi32.lib;shell32.lib;ole32.lib;oleaut32.lib;uuid.lib;odbc32.lib;odbccp32.lib;%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
   </ItemDefinitionGroup>
+  <Import Project="common.init.vcxproj.user" Condition="Exists('common.init.vcxproj.user')" />
 </Project>