Add a --symlinks argument to soong_zip

Add a --symlinks argument that defaults to true to soong_zip.
Passing --symlinks=false will cause it to follow symlinks instead
of storing them in the zip file.

Bug: 112843624
Test: glob_test.go
Test: m checkbuild
Change-Id: I4deb98daa9d4ba9f94e3d7670c117fe00381d2ba