Refactor dumpsys to expose helper apis

- allow dumpstate to interact with services without executing dumpsys binary
- Remove "NORMAL" priority from section name for backwards compatibility when switching to version 2.0

Bug: 67716082

Test: mmm -j56 frameworks/native/cmds/dumpsys && \
      adb sync data && \
      adb shell /data/nativetest/dumpsys_test/dumpsys_test && \
      adb shell /data/nativetest64/dumpsys_test/dumpsys_test && \
      printf "\n\n#### ALL TESTS PASSED ####\n"

Test: manual tests with "adb bugreport"
Change-Id: I4198333a58ffe6cb521b5cb7066520c7a3ef0675