Follow symlink when creating symbols.zip

Due to the runtime APEX, the symbols directory now contains a symlink;
./apex/com.android.runtime -> com.android.runtime.debug (or .release).

Previously, this symlink itself was included in the symbols.zip file.
And this is causing problem to the online stack tool which does not
follow the symlink in the zip file. Instead of fixing the problem in the
stack tool side, this change let the packaging routine to follow the
symlink and copy the files behind the symlink as if they were under a
directory that isn't a symlink. (i.e.
./apex/com.android.runtime/bin/dex2oat is added)

Bug: 120846816
Test: m dist with marlin (flattened) and blueline (non-flattened)
examine symbols.zip file and check that unstripped shared libraries are
found under /apex/com.android.runtime directory
Change-Id: I1d1c787a2e8ab7209410dfa2cff749a7042e21b0