community/libwpebackend-fdo: put .so symlink in main package

this is what other distros do and it is generally assumed that
it will be done (e.g. cog assumes it)
7 jobs for !20627 with libwpebackend-fdo in 5 minutes and 43 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Lint
passed #381694
docker-alpine x86_64
lint

00:00:20

 
  Build
passed #381699
docker-alpine ci-build aarch64
build-aarch64

00:01:02

passed #381700
docker-alpine ci-build armv7
build-armv7

00:00:53

passed #381698
docker-alpine ci-build ppc64le
build-ppc64le

00:01:02

passed #381697
docker-alpine ci-build s390x
build-s390x

00:01:27

passed #381696
docker-alpine ci-build x86
build-x86

00:00:29

passed #381695
docker-alpine ci-build x86_64
build-x86_64

00:00:27