Add msi, gpo, new CI and runtime/sandbox hardening

* Add msi installer via Wixtoolset
* Add PowerShell Makefile
* [MM-18135] merge lint and test step, use -quiet, clarify changing debugging port
* [MM-18135] use no sandbox, separate linting, circle 2.1
* [MM-18137] Add MSI installer job
* [MM-18137] Add windows signing
* [MM-18152] Desktop notifications (#1040)
* [MM-18345] use non-dangerous wix version
* [MM-18348] add code signing to windows build (#1044)
* [MM-18348] fix review comments
* [MM-18851] runtime/sandbox hardening (#1042)
* [MM-18906] remove GPU acceleration option from GPO settings (#1047)
* Other minor refinements

scripts/msi_installer_files_set_win64.xslt

@@ -0,0 +1,20 @@
+<xsl:stylesheet version="1.0" 
+xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+xmlns:wi="http://schemas.microsoft.com/wix/2006/wi">
+
+  <xsl:template match="@*|node()">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()" />
+    </xsl:copy>
+  </xsl:template>
+  
+  <!-- src.: https://stackoverflow.com/a/4825010/3514658 -->
+  <xsl:template match="wi:ComponentGroup[@Id='MattermostDesktopFiles']/wi:Component">
+    <xsl:copy>
+      <xsl:attribute name="Win64">yes</xsl:attribute>
+        <xsl:copy-of select="@*"/>
+      <xsl:apply-templates />
+    </xsl:copy>
+  </xsl:template>
+</xsl:stylesheet>
+