Add content_shell_apk target (and a bunch of its dependencies)

The content_shell_apk does not have the full native part that it should.
It builds, installs, starts, loads the native library, and then crashes
when it tries to access missing native parts.

This requires fixes to a bunch of little things:
1. Should only extract java files to compile from srcjars.
2. The way we were creating the single combined resources zip was wrong
because we were clobbering xml files (we should only clobber images, xml
files need to be handled more carefully). Instead of trying to properly
handle xml files, the combined zip now just puts all the different
dependencies in different folders (0/, 1/, etc) and then when packaging
we detect that type of zip and pass all the subdirs to aapt.
3. java_cpp_template with multiple sources needs to have a unique
depfile path for each source
4. jni_generator needs to clear the classlist variable in each loop of
foreach (otherwise gn complains about assigning to non-empty list)
5. a couple parts of apk native lib handling was not skipped for an apk
with no native lib

This adds a bunch of targets:
//base:base_java_test_support
//content/public/android:content_java_resources
//content/public/android:content_java
//content/public/android:content_strings_grd
//content/public/android:gesture_event_type_java
//content/public/android:page_transition_types_java
//content/public/android:popup_item_type_java
//content/public/android:result_codes_java
//content/public/android:selection_event_type_java
//content/public/android:speech_recognition_error_java
//content/public/android:top_controls_state_java
//content/public/android:screen_orientation_values_java
//content/public/android:content_gamepad_mapping_java
//content/public/android:content_jni_headers
//content/shell/android:content_shell_jni_headers
//content/shell/android:libcontent_shell_content_view (partial)
//content/shell/android:content_shell_java_resources
//content/shell/android:content_shell_java
//content/shell/android:content_shell_apk_resources
//content/shell/android:content_shell_apk
//net/android:net_java
//net/android:remote_android_keystore_aidl
//net/android:net_java_test_support
//net/android:net_javatests
//net/android:net_errors_java
//net/android:certificate_mime_types_java
//net/android:cert_verify_status_android_java
//net/android:private_key_types_java
//net/android:net_unittests_apk (disabled)

TBR=yfriedman,thestig
BUG=359249

Review URL: https://codereview.chromium.org/507523002

Cr-Commit-Position: refs/heads/master@{#293671}