Add -e argument to soong_zip to allow setting an explicit filename

soong_zip normally takes the name of the input source file as the
name of the file in the zip, which is ideal for zipping up
directories but not for constructing arbitrary zip files.  Add a
-e argument that explicitly sets the path in the zip file for
the next -f argument.

Bug: 254867347
Test: zip_test.go
Change-Id: If9d62c1a0064a485aebddf6d2a661f63f3e60b0f