we used to use different code when --framework was specified than when it was not specified, this synchronizes them to use the same code path which removes a hidden NullRef
also adds tests to cover both cases
* 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.
DOTNET_HOME is no longer required, though it is a documented override, so this change removes all unnecessary references to DOTNET_HOME from the CLI Repo.
