fix: support duplicated namespaces

[iBotPeaches]

In some applications we find duplicate namespaces. This because we move onward to common XML tools to extract/modify end up crashing.

I: Loading resource table...
I: Decoding AndroidManifest.xml with resources...
I: Regular manifest package...
[Fatal Error] :5:61: Attribute "xmlns:android" was already specified for element "manifest".

These were indeed duplicates so it was not Apktool introducing them.

➜  2664 aapt2 d xmltree 2664.apk --file AndroidManifest.xml | more
N: android=http://schemas.android.com/apk/res/android (line=4294967295)
  N: amazon=http://schemas.amazon.com/apk/res/android (line=4294967295)
    N: android=http://schemas.android.com/apk/res/android (line=4294967295)

So we maintain a mapping of prefix/uri and skip it if we encounter it again. This happens at writing time so we don't have to mess with indexes/stacks.

fixes: #2664