[ntuple] Renormalize field type names if needed in SetSchemaFromExisting

[silverweed]

Fixes #22130.

I have a local integration test for this change but I'm waiting on a user's permission to use their files.
Otherwise we can craft our own files to be merged instead.

[github-actions]

Test Results

    23 files      23 suites   3d 15h 23m 5s ⏱️
 3 874 tests  3 874 ✅ 0 💤 0 ❌
78 808 runs  78 808 ✅ 0 💤 0 ❌

Results for commit 6e804fa.

♻️ This comment has been updated with latest results.

[silverweed]

Update: the user has kindly granted us permission to use his shared files, so I uploaded the integration test.

[jblomer]

How about this approach, which would avoid another friend declaration:

We add an RFieldDescriptorBuilder::FromFieldDescriptor() method, and then we do the fixup in RNTupleDescriptor::Clone(): we replace RFieldDescriptor::Clone() with creating field descriptor builders first, and fixup the type name in that descriptor (using GetTypeNameForComparison()) before moving it into a destination field descriptor.

[silverweed]

How about this approach, which would avoid another friend declaration:

Btw I just realized the friend declaration is an unnecessary remnant from a previous experiment, I removed it. Do you think I should still try your proposal?