Auto merge of #101558 - JhonnyBillM:session-diagnostic-to-diagnostic-handler-refactor, r=davidtwco

Move and rename `SessionDiagnostic` & `SessionSubdiagnostic` traits and macros

After PR #101434, we want to:
- [x] Move `SessionDiagnostic` to `rustc_errors`.
- [x] Add `emit_` methods that accept `impl SessionDiagnostic` to `Handler`.
- [x] _(optional)_ Rename trait `SessionDiagnostic` to `DiagnosticHandler`.
- [x] _(optional)_ Rename macro `SessionDiagnostic` to `DiagnosticHandler`.
- [x] Update Rustc Dev Guide and Docs to reflect these changes. https://github.com/rust-lang/rustc-dev-guide/pull/1460

Now I am having build issues getting the compiler to build when trying to rename the macro.

<details>
  <summary>See diagnostics errors and context when building.</summary>

```
error: diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
  --> compiler/rustc_attr/src/session_diagnostics.rs:13:10
   |
13 |   #[derive(DiagnosticHandler)]
   |            ^^^^^^^^^^^^^^^^^ in this derive macro expansion
   |
  ::: /Users/jhonny/.cargo/registry/src/github.com-1ecc6299db9ec823/synstructure-0.12.6/src/macros.rs:94:9
   |
94 | /         pub fn $derives(
95 | |             i: $crate::macros::TokenStream
96 | |         ) -> $crate::macros::TokenStream {
   | |________________________________________- in this expansion of `#[derive(DiagnosticHandler)]`
   |
note: the lint level is defined here
  --> compiler/rustc_attr/src/lib.rs:10:9
   |
10 | #![deny(rustc::diagnostic_outside_of_impl)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

```

And also this one:

```
error: diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
   --> compiler/rustc_attr/src/session_diagnostics.rs:213:32
    |
213 |         let mut diag = handler.struct_span_err_with_code(
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^
```

> **Note**
> Can't find where this message is coming from, because you can see in [this experimental branch](https://github.com/JhonnyBillM/rust/tree/experimental/trying-to-rename-session-diagnostic-macro)  that I updated all errors and diags to say:
> error: diagnostics should only be created in **`DiagnosticHandler`**/`AddSubdiagnostic` impls
> and not:
> error: diagnostics should only be created in **`SessionDiagnostic`**/`AddSubdiagnostic` impls

</details>

I tried building the compiler in different ways (playing with the stages etc), but nothing worked.

## Question

**Do we need to build or do something different when renaming a macro and identifiers?**

For context, see experimental commit https://github.com/JhonnyBillM/rust/commit/f2193a98b44db3f2af77a878824b152cdf0d34a5 where the macro and symbols are renamed, but it doesn't compile.

1 files changed, 8 insertions, 8 deletions

diff --git a/compiler/rustc_monomorphize/src/errors.rs b/compiler/rustc_monomorphize/src/errors.rs
index d5f05e790d3..cf6e18c013b 100644
--- a/compiler/rustc_monomorphize/src/errors.rs
+++ b/compiler/rustc_monomorphize/src/errors.rs
@@ -1,11 +1,11 @@
 use std::path::PathBuf;
 
 use rustc_errors::ErrorGuaranteed;
-use rustc_macros::{LintDiagnostic, SessionDiagnostic};
-use rustc_session::SessionDiagnostic;
+use rustc_errors::IntoDiagnostic;
+use rustc_macros::{Diagnostic, LintDiagnostic};
 use rustc_span::Span;
 
-#[derive(SessionDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(monomorphize::recursion_limit)]
 pub struct RecursionLimit {
     #[primary_span]
@@ -19,7 +19,7 @@ pub struct RecursionLimit {
     pub path: PathBuf,
 }
 
-#[derive(SessionDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(monomorphize::type_length_limit)]
 #[help(monomorphize::consider_type_length_limit)]
 pub struct TypeLengthLimit {
@@ -32,7 +32,7 @@ pub struct TypeLengthLimit {
     pub type_length: usize,
 }
 
-#[derive(SessionDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(monomorphize::requires_lang_item)]
 pub struct RequiresLangItem {
     pub lang_item: String,
@@ -44,7 +44,7 @@ pub struct UnusedGenericParams {
     pub param_names: Vec<String>,
 }
 
-impl SessionDiagnostic<'_> for UnusedGenericParams {
+impl IntoDiagnostic<'_> for UnusedGenericParams {
     fn into_diagnostic(
         self,
         handler: &'_ rustc_errors::Handler,
@@ -72,11 +72,11 @@ pub struct LargeAssignmentsLint {
     pub limit: u64,
 }
 
-#[derive(SessionDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(monomorphize::unknown_partition_strategy)]
 pub struct UnknownPartitionStrategy;
 
-#[derive(SessionDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(monomorphize::symbol_already_defined)]
 pub struct SymbolAlreadyDefined {
     #[primary_span]