fix: rename injected entry spec if the name already exists

[IgorEisberg]

Obfuscators can exploit the new missing entry injection to prevent rebuilding by causing entry specs with identical names to be injected.
Example scenario:

res/values/public.xml:

<resources>
    <public type="attr" name="existingAttr" id="0x7f010000" />
</resources>

res/values/attrs.xml:

<resources>
    <attr name="existingAttr" format="string" />
</resources>

res/layout/issue.xml:

N: android=http://schemas.android.com/apk/res/android (line=2)
  N: app=http://schemas.android.com/apk/res-auto (line=2)
    E: merge (line=2)
        E: TextView (line=4)
          A: http://schemas.android.com/apk/res/android:layout_width(0x010100f4)=-2
          A: http://schemas.android.com/apk/res/android:layout_height(0x010100f5)=-2
          A: http://schemas.android.com/apk/res-auto:existingAttr(0x7f010001)=1

The spec 0x7f010001 is missing and the obfuscator renamed the raw attribute name to "existingAttr", which is already assigned to 0x7f010000.
Apktool will inject a generic spec with the ID 0x7f010001 and the name "existingAttr" - that's a duplicate, and the APK can't be rebuilt.

We patch this hole before obfuscators exploit it.

[IgorEisberg]

In fact, obfuscators could already have exploited this by renaming entries in the ARSC to some repeated valid name, because we hadn’t enforced name uniqueness until now.