Add VisionOS platform support to PIF.PlatformFilter (swiftlang#7448)

#### Motivation:
In the process of generating PIF, I identified a missing case for
VisionOS in the implementation of the
`[PackageConditionProtocol].toPlatformFilters()`, which led to
assertionFailure when Package's platforms included VisionOS.

#### Modifications:
- Added a new case `.visionOS` in the switch statement within the
`toPlatformFilters()` extension for `[PackageCondition]`.
- Added a new static property `visionOSFilters` within
`PIF.PlatformFilter` to define filters specific to VisionOS.

#### Result:
With these changes, PIFBuilder can now generate PIF without errors for
packages that include VisionOS as a target

(cherry picked from commit 1c68e6c)

Author: Ryu0118

Sources/XCBuildSupport/PIFBuilder.swift

@@ -1710,6 +1710,9 @@ extension [PackageCondition] {
             case .watchOS:
                 result += PIF.PlatformFilter.watchOSFilters
 
+            case .visionOS:
+                result += PIF.PlatformFilter.visionOSFilters
+
             case .linux:
                 result += PIF.PlatformFilter.linuxFilters
 
@@ -1794,6 +1797,14 @@ extension PIF.PlatformFilter {
     public static let webAssemblyFilters: [PIF.PlatformFilter] = [
         .init(platform: "wasi"),
     ]
+
+    /// VisionOS platform filters.
+    public static let visionOSFilters: [PIF.PlatformFilter] = [
+        .init(platform: "xros"),
+        .init(platform: "xros", environment: "simulator"),
+        .init(platform: "visionos"),
+        .init(platform: "visionos", environment: "simulator")
+    ]
 }
 
 extension PIF.BuildSettings {