Fix android shared_library metadata output_extension handling

Make the metadata machinery on Android use output_extension in
shared_library and similar targets if it is set, so the gathered
metadata matches the actual names of built binaries. GN shared_library
targets can set a custom 'output_extension' (for example, to explicitly
always have a .so extension and never .cr.so) and the Android metadata
machinery should work with that.

Test: set output_extension on a solib and build Android
Bug: 980569
Change-Id: I12fb2b31e753adf81bac86c07e10aa913de51969
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730155
Auto-Submit: Tomasz Śniatowski <tsniatowski@vewd.com>
Commit-Queue: Tomasz Śniatowski <tsniatowski@vewd.com>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683668}

build/config/BUILDCONFIG.gn

@@ -600,9 +600,12 @@ foreach(_target_type,
                                       1)
         _output_name = string_replace(_output_name, _magic_prefix, "", 1)
 
-        _shlib_extension = ".so"
-        if (is_component_build && _target_type != "loadable_module") {
+        if (defined(output_extension)) {
+          _shlib_extension = ".$output_extension"
+        } else if (is_component_build && _target_type != "loadable_module") {
           _shlib_extension = ".cr.so"
+        } else {
+          _shlib_extension = ".so"
         }
 
         metadata = {