fix: support implicit resource localization (#1702)

Adding a dependency on https://github.com/mapbox/mapbox-navigation-ios
caused the following error:

```
ERROR: .../rules_swift_package_manager++swift_deps+swiftpkg_mapbox_navigation_ios/BUILD.bazel:55:34: Label '@@rules_swift_package_manager++swift_deps+swiftpkg_mapbox_navigation_ios//:Sources/MapboxNavigation/Resources/Base.lproj/Navigation.storyboard' is duplicated in the 'resources' attribute of rule 'MapboxNavigation.rspm_resource_bundle'
```

This is because [this
file](https://github.com/mapbox/mapbox-navigation-ios/tree/v2.18.4/Sources/MapboxNavigation/Resources/Base.lproj)
was being added both from `desc_map` and as a discovered resource. They
aren't being deduplicated in `resources_set` because the `desc_map`
instance has localization `"Base"`, but the discovered resource had
`None` for its localization.

This PR is intended to match the behavior of [this
code](https://github.com/swiftlang/swift-package-manager/blob/2f03e7a16e2c4d08a3a16f16cca627ff53b70271/Sources/PackageLoading/TargetSourcesBuilder.swift#L312-L318)
in SPM.

Alternatively we could deduplicate the labels themselves closer to where
the build file is constructed if there's no need to track the
localizations.

---------

Co-authored-by: Chuck Grindel <chuck@revealtech.ai>

Author: jflan-dd

examples/resources_example/swift/Package.swift

@@ -7,6 +7,7 @@ let package = Package(
     dependencies: [
         .package(path: "../third_party/another_package_with_resources"),
         .package(path: "../third_party/app_lovin_sdk"),
+        .package(path: "../third_party/implicit_resource_localization"),
         .package(path: "../third_party/package_with_resources"),
         .package(path: "../third_party/package_with_resources_swift_6"),
         .package(url: "https://github.com/Iterable/swift-sdk", from: "6.5.12"),

examples/resources_example/third_party/implicit_resource_localization/Package.swift

@@ -0,0 +1,15 @@
+// swift-tools-version: 6.1
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "implicit_resource_localization",
+    defaultLocalization: "en",
+    products: [
+        .library(name: "implicit_resource_localization", targets: ["implicit_resource_localization"]),
+    ],
+    targets: [
+        .target(name: "implicit_resource_localization"),
+    ]
+)

examples/resources_example/third_party/implicit_resource_localization/README.md

@@ -0,0 +1 @@
+This package includes resources with implicit localizations using a `.lproj` resource folder.

examples/resources_example/third_party/implicit_resource_localization/Sources/Resouces/Base.lproj/Storyboard.storyboard

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<document type="com.apple.InterfaceBuilder3.Cocoa.Storyboard.XIB" version="3.0" toolsVersion="17150" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES">
+    <dependencies>
+        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="17150"/>
+        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
+    </dependencies>
+    <scenes>
+        <!--View Controller-->
+        <scene sceneID="PEd-7d-5j0">
+            <objects>
+                <viewController id="bU7-R8-ocO" sceneMemberID="viewController">
+                    <view key="view" id="tOy-S4-hL0">
+                        <rect key="frame" x="0.0" y="0.0" width="450" height="300"/>
+                        <autoresizingMask key="autoresizingMask"/>
+                    </view>
+                </viewController>
+                <customObject id="9uD-mB-xHs" userLabel="First Responder" customClass="NSResponder" sceneMemberID="firstResponder"/>
+            </objects>
+        </scene>
+    </scenes>
+</document>

examples/resources_example/third_party/implicit_resource_localization/Sources/Stub.swift

@@ -0,0 +1 @@
+// Stub file to make SPM happy

swiftpkg/internal/pkginfos.bzl

@@ -1680,10 +1680,24 @@ def _new_resource_from_discovered_resource(path):
     return _new_resource(
         path = path,
         rule = _new_resource_rule(
-            process = _new_resource_rule_process(),
+            process = _new_resource_rule_process(
+                localization = _localization_from(path),
+            ),
         ),
     )
 
+def _localization_from(path):
+    # Extract the implict localization from the path if its parent folder ends in ".lproj"
+    # https://github.com/swiftlang/swift-package-manager/blob/2f03e7a16e2c4d08a3a16f16cca627ff53b70271/Sources/PackageLoading/TargetSourcesBuilder.swift#L312-L318
+    parent_dir = paths.basename(paths.dirname(path))
+
+    (localization, extension) = paths.split_extension(parent_dir)
+
+    if extension == ".lproj":
+        return localization
+
+    return None
+
 # MARK: - Constants
 
 target_types = struct(