This allows to privatize their fields.

And change `rmeta.rs` to `rmeta/mod.rs`

This changes the mechanism of `-Z dual-proc-macro` to record the host
proc macro hash in the transistive dependency information and use it
during dependency resolution instead of resolving only by name.

Plugin search doesn't need a crate loader, only crate locator

It's a crate name after renaming, so it's entirely irrelevant to crate loading

Split off from #62855

This PR deerializes the declaration `Span` and attributes for all
procedural macros from their underlying function definitions.
This allows Rustdoc to properly render doc comments
and source links when inlining procedural macros across crates

And also the equality between `Path` and strings, because `Path` is made
up of `Symbol`s.

Allow linking to a proc macro on the target in metadata and still use a host proc macro to execute them

Instead of maybe storing its own sysroot and maybe deferring to the one
in `Session::opts`, just clone the latter when necessary so one is
always directly available. This removes the need for the getter.

Because those files are quite large, contribute significantly to peak
memory usage, but only a small fraction of the data is ever read.

resolving it as a dependency.

Fixes #46816