unify missing semantics for function calls

[mccanne]

Repro is with Zed commit 9c0f097.

Most functions don't handle missing properly.

In general, a function should return missing if any required argument is missing, e.g.,

$ zed -version
Version: v1.2.0-49-g9c0f0973

$ zed log -z
{Name:"main",Commit:0x0fafd0fa5c040fcdfd51485e0ec7f7d99af5f5ab(=ksuid.KSUID)}(=lake.BranchTip)
{id:0x0fafd0fa5c040fcdfd51485e0ec7f7d99af5f5ab(=KSUID),parent:0x0000000000000000000000000000000000000000(KSUID),retries:0(uint8),author:"[email protected]",date:2022-09-14T18:35:38.207529Z,message:"loaded 1 data object\n\n  2ElqV0SHaPKU1YDHoFyrEOImPhb 35493 records in 1663930 data bytes\n",meta:null}(=Commit)

$ zed log -z | zq -z 'yield ksuid(id)' -
error("ksuid: argument must a bytes or string type (bad argument: error(\"missing\"))")
"2ElqV2ggRY24fBQo26yJZLX4nUJ"

So the error comes from processing the branch-tip record (which has no id) instead of just skipping it.

We should audit all the functions and make sure each has proper missing semantics.