Rename base packages (#19061)

As part of applying the new versioning scheme proposed with #18938, this
renames the Python packages `iree-compiler` to `iree-base-compiler` and
`iree-runtime` to `iree-base-runtime`.
diff --git a/build_tools/pkgci/setup_venv.py b/build_tools/pkgci/setup_venv.py
index 618bb37..d0d5163 100755
--- a/build_tools/pkgci/setup_venv.py
+++ b/build_tools/pkgci/setup_venv.py
@@ -120,8 +120,8 @@
     artifact_prefix = f"{platform.system().lower()}_{platform.machine()}"
     wheels = []
     for package_stem, variant in [
-        ("iree-compiler", args.compiler_variant),
-        ("iree-runtime", args.runtime_variant),
+        ("iree-base-compiler", args.compiler_variant),
+        ("iree-base-runtime", args.runtime_variant),
     ]:
         wheels.append(
             find_wheel_for_variants(args, artifact_prefix, package_stem, variant)