Add shproj and projitems extensions to monaco_languages.json (#39246)

Both ".shproj" and ".projitems" are extensions using by Microsoft Visual
Studio for Shared Projects. The files are standard XML.

## Summary of the Pull Request

## PR Checklist

- [X] **Closes:** #39247
- [ ] **Communication:** I've discussed this with core contributors
already. If work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end user facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

## Detailed Description of the Pull Request / Additional comments

This PR simply adds two new extensions to XML for Monaco preview. Both
extensions are known by Visual Studio.

## Validation Steps Performed

No automated test. Monaco has a configuration file that works like a
dictionary to define supported languages and their extensions. I added
the two extensions to this file for XML language.

---------

Co-authored-by: Gordon Lam (SH) <yeelam@microsoft.com>

src/Monaco/monacoSpecialLanguages.js

@@ -7,7 +7,7 @@ import { srtDefinition } from './customLanguages/srt.js';
 export async function registerAdditionalLanguages(monaco){
     await languageDefinitions();
     registerAdditionalLanguage("cppExt", [".ino", ".pde"], "cpp", monaco);
-    registerAdditionalLanguage("xmlExt", [".wsdl", ".csproj", ".vcxproj", ".vbproj", ".fsproj", ".resx", ".resw"], "xml", monaco);
+    registerAdditionalLanguage("xmlExt", [".wsdl", ".projitems", ".csproj", ".fsproj", ".shproj", ".vcxproj", ".vbproj", ".resx", ".resw"], "xml", monaco);
     registerAdditionalLanguage("txtExt", [".sln", ".log", ".vsconfig", ".env", ".ahk", ".ion"], "txt", monaco);
     registerAdditionalLanguage("razorExt", [".razor"], "razor", monaco);
     registerAdditionalLanguage("vbExt", [".vbs"], "vb", monaco);