compiler: follow-on fix for finalizing imported methods

compiler: follow-on fix for finalizing imported methods

    This patch is a revision to CL 185518, which added code to perform
    finalization of methods on types created by the importer and not
    directly reachable until inlining is done.

    The original fix invoked the finalization code at the end of
    Import::read_types(), but it turns out this doesn't handle the case
    where a type with methods is read in due to a reference from something
    later in the export data (a function or variable). The fix is to move
    the import finalization call to the end of Import::import().

    Testcase for this bug is in CL 187057.

    Fixes golang/go#33219.

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/187058

From-SVN: r273713