Rename "install/" to "pkg/" and fix macOS bundling

[angela28chen]

Notable changes:

• Rename install/ to pkg/ and have separate folders within for host tools, device resources, and plugins
• Change logic for locating resources
  • Remove CMAKE_GENERATED_INSTALL_DIR_PATH and predict the location of different resources relative to the location of the host tool.
  • Split the resolving logic into separate functions that forces the caller to specify which type of resource they are looking for (so that the caller doesn't need knowledge of the layout of resources dir)
  • Using device_resources library to expose related CMAKE_GENERATED_* values, to try and keep fewer libraries regenerated upon SHA changing
• Fix the mac install/deploy process, moving some processes (macdeployqt, signing, copying of plugin folders and etc.) out of cmake's install stage and into a separate bash script. This is done because cmake's install portion is inflexible (difficult to even add log messages) and it's error-prone to insert blocks of code.
• Changed BUILD.md to reference scripts rather than repeat their contents

PSAs:

• Make sure to install with cmake right after building and before running any tests, or Dive might not be able to locate resources
• dive_profiling_plugin and other external plugins should be copy pasted into pkg/plugins/ now. Best is to do this step when setting up repo & don't delete pkg/plugins while rebuilding

[angela28chen]

Should be identical to #690, just using a new PR because the old one seems to be bugged.