Remove last remaining !go1.22 build tag

[copybara-service]

Remove last remaining !go1.22 build tag

The last remaining !go1.22 build is protecting the definition of
pkg/sync.maptype, which is a copy of runtime.maptype. We need to ensure these
definitions match so we can safely access the hasher field.

At its core, this CL achieves this check by ensuring that
unsafe.Offsetof(maptype{}.Hasher) matches the offset in the runtime version of
the type.

Several things happen along the way to achieve this:

• As of May 2023, runtime.maptype is actually a type alias for
  internal/abi.MapType. checkoffset was failing to record the offsets because it
  skipped type aliases for no good reason. Simply removing the type alias check
  is sufficient to make type aliases work. (This part of the CL is technically
  unnecessary because this CL ultimately references internal/abi.MapType
  directly in anticipation of removal of the type alias. But there is no reason
  not to allow type aliases).

• The checkconst / checkoffset regexp unintentionally does not allow / in
  package paths, even though the rest of the package supports /. Fix this.

• checkconst was comparing the literal AST expression string against the
  runtime value (i.e., "unsafe.Offsetof(maptype{}.Hasher)" vs "72", which fails
  comparison. Switch to getting the resolved constant value from the type
  checker.

• nogo/check.importer only loads package facts on direct import (stored in
  importer.cache). If a package is not directly imported ImportPackageFact will
  not find the facts. Typically packages need to ensure they directly depend on
  packages they want facts from (e.g., pkg/sync has a dummy import of runtime in
  runtime.go). This doesn't work for internal/abi because we cannot directly
  import an internal package. Work around this as a hack by unconditionally
  "importing" internal/abi when analyzing any package.

With regard to the last point, not that the nogo/defs.bzl nogo integration only
provides facts from the direct dependencies and the entire stdlib (since the
stdlib is analyzed as one bundle). So this trick only works for a stdlib
package. A bazel package indirect dependency would be missing facts altogether.