Auto merge of #96301 - notriddle:notriddle/synthetic-impl-prim, r=GuillaumeGomez

rustdoc: make primitive synthetic impls for correct doc module

This improves the accuracy of libcore primitive docs, which was missing the blanket and auto impls for most primitive types. To test this, compare nightly [libcore::str] docs, which lack auto traits like Send, with [std::str] docs, which show them.

[libcore::str]: https://doc.rust-lang.org/nightly/core/primitive.str.html
[libstd::str]: https://doc.rust-lang.org/nightly/std/primitive.str.html

It also avoids getting synthetic impls for primitive types on crates that do not actually show them.

<details>

<summary>Before and After trace logs</summary>

## Before

	[notriddle@deep-thought test-dingus]$ RUSTDOC_LOG=rustdoc=trace rustdoc +nightly test.rs 2>&1 | grep -E 'get_blanket_impls\('
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(Whatever)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(isize)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls([T])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls([u8])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls([T])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls([u8])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(char)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(u128)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(u16)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(i128)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(i16)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(str)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(str)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(f64)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(f64)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(u64)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(u8)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(i64)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(i8)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(*const T)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(*mut T)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(*const [T])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(*mut [T])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls([T; N])
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(bool)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(f32)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(f32)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(u32)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(usize)
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(i32)

## After

	[notriddle@deep-thought test-dingus]$ RUSTDOC_LOG=rustdoc=trace rustdoc +dev test.rs 2>&1 | grep -E 'get_blanket_impls\('
	TRACE rustdoc::clean::blanket_impl get_blanket_impls(Whatever)

</details>

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