Fix some issues with multi-target extraction

[sonmarcho]

This PR was AI generated and I'm not asking to merge it: I'm opening it because it is informative.
It solves #1130

Importantly, you will note that attributes, spans and source text led to item duplication, and the agent had to filter them to solve the issue. This is of course not what we want to do, but it seems the fix below is enough to make the deduplication work. About attributes specifically: Aeneas relies on some Unknown attributes (such as verify::test) so we can't just clear them (we need a merge operation, and maybe we need to introduce the notion of target-specific attribute?).

[Nadrieril]

Can you add the test case from #1130 to the test suite?

[sonmarcho]

Can you add the test case from #1130 to the test suite?

Does that mean you want to merge this PR? (yes I can do)

[sonmarcho]

I added the test

[Nadrieril]

Does that mean you want to merge this PR?

Mostly I wanted to see the new output. If you remove the attribute and source_text stripping, does this PR still fix #1130? (I'd expect it to)

[sonmarcho]

When removing the attribute and source_text stripping I get the following diff on the multi-targets-3-dedup.outfile:

-pub fn core::clone::impls::{impl core::clone::Clone for u32}::clone<'_0>(_1: &'_0 u32) -> u32
+pub fn core::clone::impls::{impl core::clone::Clone::aarch64-apple-darwin for u32}::clone::aarch64-apple-darwin<'_0>(_1: &'_0 u32) -> u32
 = <opaque>
 
+pub fn core::clone::impls::{impl core::clone::Clone::x86_64-pc-windows-msvc for u32}::clone::x86_64-pc-windows-msvc<'_0>(_1: &'_0 u32) -> u32
+= <opaque>
+
+pub fn core::clone::impls::{impl core::clone::Clone::i686-pc-windows-msvc for u32}::clone::i686-pc-windows-msvc<'_0>(_1: &'_0 u32) -> u32
+= <opaque>
+
+pub fn core::clone::impls::{impl core::clone::Clone::x86_64-pc-windows-msvc for u32}::clone<'_0>(_1: &'_0 u32) -> u32
+= target_dispatch {
+    x86_64-pc-windows-msvc => core::clone::impls::{impl core::clone::Clone::x86_64-pc-windows-msvc for u32}::clone::x86_64-pc-windows-msvc<'_0>,
+    aarch64-apple-darwin => core::clone::impls::{impl core::clone::Clone::aarch64-apple-darwin for u32}::clone::aarch64-apple-darwin<'_0>,
+    i686-pc-windows-msvc => core::clone::impls::{impl core::clone::Clone::i686-pc-windows-msvc for u32}::clone::i686-pc-windows-msvc<'_0>,
+}
+
 fn test_crate::clone_it<'_0>(x_1: &'_0 u32) -> u32
 {
     let _0: u32; // return
@@ -9,7 +22,7 @@ fn test_crate::clone_it<'_0>(x_1: &'_0 u32) -> u32
 
     storage_live(_2)
     _2 = &(*x_1)
-    _0 = core::clone::impls::{impl core::clone::Clone for u32}::clone<'4>(move _2)
+    _0 = core::clone::impls::{impl core::clone::Clone::x86_64-pc-windows-msvc for u32}::clone<'4>(move _2)
     storage_dead(_2)
     return
 }