Memory usage improvements in build (#2626)

* Use a WorkspaceContext in dotnet-build to cache project data across
multiple compilations in a single build action
* Dramatically reduce string and object duplication by introducing a
"Symbol Table" that shares instances of NuGetVersion, NuGetFramework,
VersionRange and string across multiple lock-file parses

Test Results:
* Testing was done by compiling Microsoft.AspNetCore.Mvc (and it's
dependencies) and taking memory snapshots after each compilation in
dotMemory
* We used to allocate ~3MB and deallocate ~2.5MB on EACH compilation in
a single build action. This has been reduced to ~120KB
allocated/deallocated
* After introducing WorkspaceContext, total memory usage spiked from 6MB
across the whole build action to about 13MB, introducing the symbol
table dropped it back to about 5-6MB.

src/dotnet/commands/dotnet-publish/Program.cs

@@ -5,6 +5,7 @@ using System;
 using System.IO;
 using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
 
 namespace Microsoft.DotNet.Tools.Publish
 {
@@ -44,6 +45,8 @@ namespace Microsoft.DotNet.Tools.Publish
                 publish.VersionSuffix = versionSuffix.Value();
                 publish.ShouldBuild = !noBuild.HasValue();
 
+                publish.Workspace = WorkspaceContext.Create(versionSuffix.Value(), designTime: false);
+
                 if (string.IsNullOrEmpty(publish.ProjectPath))
                 {
                     publish.ProjectPath = Directory.GetCurrentDirectory();