Small fixes to DumpManager

1) Use a TreeMap instead of an ArrayMap for dumpables and buffers to ensure consistent and predictable dump order across bugreports.
2) Instead of selecting just the first dumpable to match the target string, select the one with the shortest name; this guaruntees that an exact match will always be returned.

Test: dumpsysui --list (observe: dumpables and buffers are in alphabetical order)
Test: dumpsysui Log (observe: dumps QSLog instead of WifiTableLog)
Test: atest DumpManagerTest
Fixes: 252783246
Change-Id: Ifbdf3428b9343e1146e39e20f65a5897f6821f90