[meta] TClass: prefer typeid=>TClass map values with less Double32_t v2

[dpiparo]

Reformulation of https://github.com/root-project/root/pull/12480

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Both Foo and Foo<Double32_t> have the same typeid. Before this commit, TClass::GetClass(typeid(Foo)) would return whatever was registered last. This is not "stable"; it depends on which branch is accessed first, or which TClass::GetClass call happens first, or which library is loaded first.

Make this more reporducible by consistently preferring types will less Double32_t / Float16_t occurrences uin the typename.

While at this, only remove a TClass from the typeid=>TClass map if it really is the value for the typename.

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This PR fixes #12509

[github-actions[bot]]

Test Results

    18 files      18 suites   4d 4h 9m 17s ⏱️  2 699 tests  2 691 ✅ 1 💤 7 ❌ 46 128 runs  46 121 ✅ 0 💤 7 ❌

For more details on these failures, see this check.

Results for commit 31d6e774.

:recycle: This comment has been updated with latest results.

[dpiparo]

Thanks @pcanal for having another look.