Add a PackageArgs class in preparation for REPO.bazel

- Created a PackageArgs class that stores the values passed to the attrs of the `package()` function, so that they can be applied to a package builder in one go
  - These attr values used to be applied as soon as each attr is processed (i.e. evaluated). We can't do that anymore for repo(), since at the time of REPO.bazel evaluation, the package hasn't started being built yet.
  - Instead of storing the individual fields, Package now just holds on to a PackageArgs object.
  - In a follow-up CL, we store all the repo() values in a PackageArgs class, and apply those before the package() ones.
- Also removed `Package#isDefaultVisibilitySet` as nobody calls it anymore.

Work towards #18077

PiperOrigin-RevId: 539728608
Change-Id: Ie4a081fa0e52e833ac2a6be50033f95728da3a9b

src/main/java/com/google/devtools/build/lib/packages/BuildGlobals.java

@@ -121,7 +121,7 @@ public NoneType licenses(
     PackageContext context = PackageFactory.getContext(thread);
     try {
       License license = BuildType.LICENSE.convert(licensesList, "'licenses' operand");
-      context.pkgBuilder.setDefaultLicense(license);
+      context.pkgBuilder.mergePackageArgsFrom(PackageArgs.builder().setLicense(license));
     } catch (ConversionException e) {
       context.eventHandler.handle(
           Package.error(thread.getCallerLocation(), e.getMessage(), Code.LICENSE_PARSE_FAILURE));
@@ -144,7 +144,7 @@ public NoneType distribs(Object object, StarlarkThread thread) throws EvalExcept
     try {
       Set<DistributionType> distribs =
           BuildType.DISTRIBUTIONS.convert(object, "'distribs' operand");
-      context.pkgBuilder.setDefaultDistribs(distribs);
+      context.pkgBuilder.mergePackageArgsFrom(PackageArgs.builder().setDistribs(distribs));
     } catch (ConversionException e) {
       context.eventHandler.handle(
           Package.error(