Fix Issue 22218 - Dynamic casts across binary boundaries can easily fail

[kinke]

A rebase/reboot of #2828.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22218	major	Dynamic casts across binary boundaries can easily fail

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + druntime#3543"

[kinke]

Not sure

• whether the null-checks are really required here, or are better moved to the few call sites potentially passing a null, (edit: moved)
• whether the extra name check should be restricted to shared druntime (*.{so,dll}) only, in order not to slow down dynamic casts with static druntime, assuming static druntime isn't used for multiple D binaries in a process (with Windows exception for DMD) - see Fix exceptions and dynamic casts across dll boundaries #2828 (comment).