raco pkg {install,update}: guard against ill-formed arguments

Parsing a package source/name for scope inference should
report errors in the source/name syntax.

Closes PR 14026
raco setup: fix several triggers for building a doc index

In particular, fix various triggers that affect installing and
uninstalling packages.
fixes for binary-package stripping

Avoid duplicate `assume-virtual-sources` definitions, add
`assume-virtual-sources` as needed in top-level collections
within a package.
raco pkg tests: adjust to make tests less dependent on installation

In particular, instead of relying on the default scope as "user"
set up an installation with an indirection that configures the
scope to "user".
fixup for showing dependencies during update