feat: commonizes several FDv2 related types in Internal (#141)

Moves Selector into Common and updates a couple imports to use it.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Upgrades `launchdarkly-java-sdk-common` and relocates the FDv2
`Selector` type, which can cause compile-time breaks for any code still
importing the internal package and may subtly change semantics via the
common implementation.
> 
> **Overview**
> FDv2 now uses the shared `com.launchdarkly.sdk.fdv2.Selector` type:
internal FDv2 sources (`FDv2ChangeSet`, `FDv2ProtocolHandler`) update
imports accordingly and the old `internal.fdv2.sources.Selector` class
is removed.
> 
> Also bumps the `launchdarkly-java-sdk-common` dependency from `2.1.2`
to `2.4.0` to supply the commonized FDv2 types.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
f478282. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->



BEGIN_COMMIT_OVERRIDE
feat: commonizes several FDv2 related types
END_COMMIT_OVERRIDE

Author: tanderson-ld

lib/shared/internal/buildSrc/src/main/kotlin/Dependencies.kt

@@ -4,7 +4,7 @@
 
 object Versions {
     const val gson = "2.13.1"
-    const val launchdarklyJavaSdkCommon = "2.1.2"
+    const val launchdarklyJavaSdkCommon = "2.4.0"
     const val launchdarklyLogging = "1.1.1"
     const val okhttp = "4.12.0"
     const val testHelpers = "1.2.0"

lib/shared/internal/src/main/java/com/launchdarkly/sdk/internal/fdv2/sources/FDv2ChangeSet.java

@@ -1,6 +1,7 @@
 package com.launchdarkly.sdk.internal.fdv2.sources;
 
 import com.google.gson.JsonElement;
+import com.launchdarkly.sdk.fdv2.Selector;
 
 import java.util.Collections;
 import java.util.List;

lib/shared/internal/src/main/java/com/launchdarkly/sdk/internal/fdv2/sources/FDv2ProtocolHandler.java

@@ -1,5 +1,6 @@
 package com.launchdarkly.sdk.internal.fdv2.sources;
 
+import com.launchdarkly.sdk.fdv2.Selector;
 import com.launchdarkly.sdk.internal.fdv2.payloads.DeleteObject;
 import com.launchdarkly.sdk.internal.fdv2.payloads.Error;
 import com.launchdarkly.sdk.internal.fdv2.payloads.FDv2Event;