actions: vendor sources with submodules for releases

[widlarizer]

We like submodules for SBOM reasons and prefer them over in-repo vendored libraries. However this creates a burden on users with needs for gitless workflows who have to take our (yosys) source tarball, drop in our other (yosys-abc) source tarball, manually check submodules versions at the git tag, download those, and only then build yosys. An alternate solution is to add Makefile targets like curl-abc #4472 but that needs per-submodule work. This PR adds a workflow which on main commits creates a source tarball artifact including submodule sources

• instruct users of vendored dependencies that licenses in abc/ and libs/* apply to those components
• eliminate zeroes that prevent libs/cxxopts from being visible

[KrystalDelusion]

Is the idea here to replace the current ABC tarball with this combined tarball for inclusion in release?

[widlarizer]

I don't know, but the availability of an all-inclusive tarball is kind of orthogonal to whether there is still a need to provide yosys-abc seperately in the yosys repo

[KrystalDelusion]

I guess the replacement is less what I was asking, and more is retention-days: 1 because the intention is for it to be added to releases, as opposed to being generally available for the most recent commit

[widlarizer]

Yes, 1 because the intention is to be added to releases. My intention is to be able to run it manually actually, so:

• re-add workflow_dispatch