idmap2: add sections to 'idmap2 dump' output

With the introduction of the debug info, the output of 'idmap2 dump' is
becoming messy. Add sections to combat this.

Example output:

  $ idmap2 create \
        --target-apk-path frameworks/base/cmds/idmap2/tests/data/target/target.apk \
        --overlay-apk-path frameworks/base/cmds/idmap2/tests/data/overlay/overlay.apk \
        --idmap-path /tmp/a.idmap \
        --policy public \
        --policy oem

  $ idmap2 dump --idmap-path /tmp/a.idmap
  Paths:
      target apk path  : frameworks/base/cmds/idmap2/tests/data/target/target.apk
      overlay apk path : frameworks/base/cmds/idmap2/tests/data/overlay/overlay.apk
  Debug info:
      I fulfilled_policies=oem|public enforce_overlayable=true
      W failed to find resource "integer/not_in_target" in target resources
  Mapping:
      0x7f010000 -> 0x7f010000 integer/int1
      0x7f02000c -> 0x7f020000 string/str1
  [...]

Test: idmap2_tests
Change-Id: Ie42f97484b31af0c0b34f1856d321533904dbf7a