Since 3.16, LSP supports the capability `insertReplaceSupport`. This
allows textEdit to be an `InsertReplaceEdit` see:
(https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#insertReplaceEdit)

This patch adds support for this capability, and uses the `replace`
field of the `InsertReplaceEdit`. Original functionality (ie.
`TextEdit`) is preserved.

The benefits of this were originally discussed here:
https://github.com/joaotavora/eglot/discussions/1456, but this is a summary:

Consider this file:

```
const Foo = struct {
    correct_name: u32,
};

fn example(foo: Foo) u32 {
    return foo.correct_name;
}
```

1. Place the cursor on 6:22 (the _ in correct_name)
2. Backspace once to delete the t
3. Receive the following LSP message: `<-- textDocument/completion[20] {"jsonrpc":"2.0","id":20,"result":{"isIncomplete":false,"items":[{"label":"correct_name","kind":5,"detail":"u32","documentation":{"kind":"plaintext","value":""},"sortText":"2_correct_name","textEdit":{"range":{"start":{"line":5,"character":15},"end":{"line":5,"character":21}},"newText":"correct_name"}}]}}`
4. Accept the completion
5. The buffer now contains `    return foo.correct_name_name;` on line 6

I expected it to replace the entire token, resulting in `    return foo.correct_name;`.

Indeed with this patch applied (and an LSP that supports the
capability), the behaviour I expected is now what happens.

This is the first real elisp that I've written besides configuration, so
Thanks!
Casey


In GNU Emacs 30.0.91 (build 1, x86_64-w64-mingw32) of 2024-10-17 built
 on DESKTOP-EK25TL1
Repository revision: 50620e96d763bd21854a95c580b572687eebc319
Repository branch: eglot_insert_replace_edit
Windowing system distributor 'Microsoft Corp.', version 10.0.19045
System Description: Microsoft Windows 10 Pro (v10.0.2009.19045.5011)

Configured using:
 'configure -prefix=/e/dev/emacs-src --without-dbus --without-pop
 --with-native-compilation --with-xml2 --with-wide-int
 --without-compress-install 'CFLAGS=-O2 -mtune=native -march=native
 -fomit-frame-pointer -ftree-vectorize'
 PKG_CONFIG_PATH=/mingw64/lib/pkgconfig:/mingw64/share/pkgconfig'