Add changelog entry for error message changes (#20753)

Co-authored-by: Dennis Korpel <dennis@sarc.nl>

changelog/dmd.error-messages.dd

@@ -0,0 +1,45 @@
+Many error messages have changed
+
+Some changes have been made without being associated to a reported issue:
+
+Error messages for `@safe` violations now consistently mention they are related to `@safe` functions (or default functions with `-preview=safer`).
+In general, function attributes that failed to infer have a more compact error message:
+
+---
+/*
+BEFORE:
+app.d(8): Error: function `attributediagnostic_nothrow.gc1` is not `nothrow`
+app.d(2):        which wasn't inferred `nothrow` because of:
+app.d(2):        `object.Exception` is thrown but not caught
+
+AFTER:
+app.d(8): Error: function `attributediagnostic_nothrow.gc1` is not `nothrow`
+app.d(2):        and `object.Exception` being thrown but not caught makes it fail to infer `nothrow`
+*/
+---
+
+Match levels are now mentioned on ambiguous overloads: [#20637](https://github.com/dlang/dmd/pull/20637)
+
+---
+/*
+BEFORE:
+Error: `app.bar` called with argument types `(string)` matches both:
+
+AFTER:
+Error: `app.bar` called with argument types `(string)` matches multiple overloads after implicit conversions:
+*/
+---
+
+When there's no operator overload found for a type, a new supplemental message points to the declaration.
+
+---
+/*
+app.d(8): Error: no `[]` operator overload for type `U`
+app.d(6):        `app.U` declared here
+*/
+---
+
+Furthermore:
+
+- D1 operator overloading functions (`opAdd`, `opDot`) are completely removed and no longer mentioned in error messages specifically.
+- Class allocators (`auto new() {}`) are not only a semantic error, but no longer being parsed