Switch dackka from main to androidx-main revision

This leaves tools/external/gradle on the dackka-main-dev revision
because the androidx-main revision is on gradle 8.13, but dackka is only
on gradle 8.11.

Bug: 409358824
Change-Id: Idd9d8405409eaa730c2a0669542a320e420ab64a

default.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<manifest>
+
+  <remote  name="aosp"
+           fetch=".."
+           review="https://android-review.googlesource.com/" />
+  <default revision="androidx-main"
+           remote="aosp"
+           sync-j="8" />
+  <project path="tools/dokka-devsite-plugin" name="platform/tools/dokka-devsite-plugin" />
+  <project path="prebuilts/androidx/external" name="platform/prebuilts/androidx/external" clone-depth="1"/>
+  <project path="prebuilts/androidx/internal" name="platform/prebuilts/androidx/internal" clone-depth="1"/>
+  <project path="tools/repohooks" name="platform/tools/repohooks" groups="adt-infra,cts,eclipse,motodev,pdk,tools,tradefed" />
+  <project path="tools/external/gradle"
+    name="platform/tools/external/gradle"
+    revision="dackka-main-dev"
+    groups="tools"
+    clone-depth="1" />
+  <repo-hooks in-project="platform/tools/repohooks" enabled-list="pre-upload" />
+  <project
+    path="prebuilts/jdk/jdk21"
+    name="platform/prebuilts/jdk/jdk21"
+    groups="pdk"
+    clone-depth="1" />
+</manifest>