Remove P<> from visit_s in ast MutVisitor

[maxcabrajac]

On #128974, one divergence I found between versions of the trait were P<> wrappers on some types on the mutable one.
Some are really easy to remove, while others are not.
This PR tries to remove them.

r? @petrochenkov

related to #128974

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[petrochenkov]

(The PR was marked as a draft, so I assumed you want to try removing the rest of P<>s.)

[maxcabrajac]

Yup, that was the idea... But I'm starting to think this might not be a good one. From the Vistor's perspective it surely is, but when I looked at how rustc_expand heavily uses substitution on this P<>s it seems not to be great to remove them.

I'll look deeper into it on the weekend and keep you up to date!

If I end up finding a way to remove them from the visits then its best that we do another perf test.

[maxcabrajac]

For now, I removed P<>s from all visits, but this just pushed the problem into rustc_expand. What I see as the problem now is calling .into_inner() on the P<>s we get from .make_*() methods. A better approach is to change them to return T instead of P<T>. This would possibly remove some memory allocations, which I see as a good thing!

[bors]

☔ The latest upstream changes (presumably #131284) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

The job x86_64-gnu-llvm-18 failed! Check out the build log: (web) (plain)

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##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
---- [ui] tests/ui-fulldeps/pprust-expr-roundtrip.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui-fulldeps/pprust-expr-roundtrip.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(FALSE)" "-O" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/pprust-expr-roundtrip/a" "-A" "internal_features" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers"
--- stderr -------------------------------
error[E0053]: method `visit_expr` has an incompatible type for trait
##[error]  --> /checkout/tests/ui-fulldeps/pprust-expr-roundtrip.rs:201:33
   |
   |
LL |     fn visit_expr(&mut self, e: &mut P<Expr>) {
   |                                 ^^^^^^^^^^^^ expected `rustc_ast::Expr`, found `P<rustc_ast::Expr>`
   |
   = note: expected signature `fn(&mut RemoveParens, &mut rustc_ast::Expr)`
              found signature `fn(&mut RemoveParens, &mut P<rustc_ast::Expr>)`
   |
   |
LL |     fn visit_expr(&mut self, e: &mut rustc_ast::Expr) {

error[E0053]: method `visit_expr` has an incompatible type for trait
##[error]  --> /checkout/tests/ui-fulldeps/pprust-expr-roundtrip.rs:214:33
   |
   |
LL |     fn visit_expr(&mut self, e: &mut P<Expr>) {
   |                                 ^^^^^^^^^^^^ expected `rustc_ast::Expr`, found `P<rustc_ast::Expr>`
   |
   = note: expected signature `fn(&mut AddParens, &mut rustc_ast::Expr)`
              found signature `fn(&mut AddParens, &mut P<rustc_ast::Expr>)`
   |
   |
LL |     fn visit_expr(&mut self, e: &mut rustc_ast::Expr) {

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0053`.