[usd] fix dll path and update to 20.08

[ousttrue]

Describe the pull request

• fix dll path in cmake for find_package
• fix dll path in for runtime plug load
• version up to 20.08(usd-20.05 fixed release build issue: Release build of USD on Win10 will not execute usdview, but debug build of USD works fine. PixarAnimationStudios/OpenUSD#960)
• add usage( find_package(usd) => find_package(pxr) )

The following Debug and Release work fine.

#define NOMINMAX
#include <pxr/usd/usd/stage.h>
#include <pxr/usd/sdf/path.h>
#include <pxr/usd/usdGeom/sphere.h>

int main()
{
    auto stage = pxr::UsdStage::CreateInMemory();
    auto sphere = pxr::UsdGeomSphere::Define(stage, pxr::SdfPath("/TestSphere"));
    auto root = stage->GetRootLayer();
    root->Export("test_sphere.usda");
    return 0;
}

[LilyWangL]

Thanks for your PR. Now usd build failed on Linux and MACOS with the following error:

CMake Error at /mnt/vcpkg-ci/downloads/tools/cmake-3.17.2-linux/cmake-3.17.2-Linux-x86_64/share/cmake-3.17/Modules/FindPackageHandleStandardArgs.cmake:164 (message):
  Could NOT find TBB (missing: tbb) (found version "2020.1")
Call Stack (most recent call first):
  /mnt/vcpkg-ci/downloads/tools/cmake-3.17.2-linux/cmake-3.17.2-Linux-x86_64/share/cmake-3.17/Modules/FindPackageHandleStandardArgs.cmake:445 (_FPHSA_FAILURE_MESSAGE)
  cmake/modules/FindTBB.cmake:277 (find_package_handle_standard_args)
  /agent/_work/1/s/scripts/buildsystems/vcpkg.cmake:493 (_find_package)
  cmake/defaults/Packages.cmake:112 (find_package)
  CMakeLists.txt:23 (include)

[ousttrue]

All green 👍
TBB handling is difficult.

[ras0219-msft]

Thanks for the PR!

[ousttrue]

cmake TARGET_PATH fixed.
CI x86_windows #13722

[ras0219-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ousttrue]

/azp run

[azure-pipelines]

Commenter does not have sufficient privileges for PR 13687 in repo microsoft/vcpkg

[strega-nil]

Gonna let this run through CI after merging with master, then merge :)