Auto merge of #18032 - DropDemBits:sed-tree-edits, r=davidbarsky

internal: Add preliminary `SyntaxEditor` functionality

Related to #15710

Implements a `SyntaxEditor` interface to abstract over the details of modifying syntax trees, to both simplify creating new code fixes and code actions, as well as start on the path of getting rid of mutable syntax nodes.

`SyntaxEditor` relies on `SyntaxMappingBuilder`s to feed in the correct information to map AST nodes created by `make` constructors, as `make` constructors do not guarantee that node identity is preserved. This is to paper over the fact that `make` constructors simply re-parse text input instead of building AST nodes from the ground up and re-using the provided syntax nodes.

`SyntaxAnnotation`s are used to find where syntax elements have ended up after edits are applied. This is primarily useful for the `add_{placeholder,tabstop}` set of methods on `SourceChangeBuilder`, as that currently relies on the nodes provided being in the final syntax tree.

Eventually, the goal should be to move this into the `rowan` crate when we move away from mutable syntax nodes, but for now it'll stay in the `syntax` crate.

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Closes #14921 as `SyntaxEditor` ensures that all replace changes are disjoint
Closes #9649 by implementing `SyntaxAnnotation`s

src/tools/rust-analyzer/crates/syntax/src/lib.rs

@@ -40,6 +40,7 @@ pub mod ast;
 #[doc(hidden)]
 pub mod fuzz;
 pub mod hacks;
+pub mod syntax_editor;
 pub mod ted;
 pub mod utils;