Pretty print SBox manifest files to make them easier to read

When debugging problems with, or just modifying a ninja rule that uses
the SBox it is often necessary to read the manifest file. This change
makes them easier to read by pretty printing them onto multiple lines
with a small but clear indent.

This increased the size of the following file by abot 6% from 66K to
70K bytes:
    out/soong/.intermediates/packages/modules/Wifi/framework/framework-wifi.stubs.source.system/android_common/metalava.sbox.textproto

Test: m out/soong/.intermediates/packages/modules/Wifi/framework/framework-wifi.stubs.source.system/android_common/metalava.sbox.textproto
      less out/soong/.intermediates/packages/modules/Wifi/framework/framework-wifi.stubs.source.system/android_common/metalava.sbox.textproto
Change-Id: Icfadeaad1c6334bd0010128f4437669f35822850