Add build and test environment setup scripts, update developer guide

scripts/cli-test-env.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) .NET Foundation and contributors. All rights reserved.
+# Licensed under the MIT license. See LICENSE file in the project root for full license information.
+#
+
+SOURCE="${BASH_SOURCE[0]}"
+while [ -h "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symlink
+  DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
+  SOURCE="$(readlink "$SOURCE")"
+  [[ "$SOURCE" != /* ]] && SOURCE="$DIR/$SOURCE" # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
+done
+
+REPO_ROOT="$( cd -P "$( dirname "$SOURCE" )/../" && pwd )"
+
+RID=linux-x64
+
+STAGE2_DIR=$REPO_ROOT/bin/2/$RID/dotnet
+export PATH=$STAGE2_DIR:$PATH
+
+
+export DOTNET_SKIP_FIRST_TIME_EXPERIENCE=1
+export DOTNET_MULTILEVEL_LOOKUP=0
+
+export NUGET_PACKAGES=$REPO_ROOT/.nuget/packages
+export TEST_PACKAGES=$REPO_ROOT/bin/2/$RID/test/packages
+export TEST_ARTIFACTS=$REPO_ROOT/bin/2/$RID/test/artifacts
+export PreviousStageProps=$REPO_ROOT/bin/2/$RID/PreviousStage.props