This allows soong to read constant information from starlark files. At package initialization time, soong will read build/bazel/constants_exported_to_soong.bzl, and then make the variables from that file available via starlark_import.GetStarlarkValue(). So to import a new variable, it must be added to constants_exported_to_soong.bzl and then it can be accessed by name.
Only constant information can be read, since this is not a full bazel execution but a standalone starlark interpreter. This means you can't use bazel contructs like rule, provider, select, glob, etc.
All starlark files that were loaded must be added as ninja deps that cause soong to rerun. The loaded files can be retrieved via starlark_import.GetNinjaDeps().