Snippet transform `camelcase` not working well.
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- VS Code Version: 1.65.2
- OS Version: Darwin x64 19.6.0

Steps to Reproduce:

1. Create a code snippet like this.

```json
{
	"TS -> Inject Service": {
		"scope": "typescript",
		"description": "Constructor Injection Pattern",
		"prefix": "@inject",
		"body": "@inject(${1/(.*)/I${1}Token/}) private readonly ${1/(.*)/${1:/camelcase}/}: I${1},$0"
	}
}
```

2. Using the snippet. 

![camelcase](https://user-images.githubusercontent.com/24731539/160342428-b0d6e71e-f472-4c34-8ce3-48b28ffc7e51.gif)

As I as concerned, the camelcase of `PathService` should be `pathService`. However, the result is `pathservice`. 

https://github.com/microsoft/vscode/blob/049b0e564b6bc1fcc07e9a39b727bca9836274f4/src/vs/editor/contrib/snippet/browser/snippetParser.ts#L404-L418

The implementation doesn't seems to tackle it well. 

I'd like to help if you could be so nice to give me a hint to fix the problem. 😃 

Snippet transform `camelcase` not working well.
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<!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ -->
<!-- 🕮 Read our guide about submitting issues: https://github.com/microsoft/vscode/wiki/Submitting-Bugs-and-Suggestions -->
<!-- 🔎 Search existing issues to avoid creating duplicates. -->
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<!-- 🔧 Launch with `code --disable-extensions` to check. -->
Does this issue occur when all extensions are disabled?: Yes/No

<!-- 🪓 If you answered No above, use 'Help: Start Extension Bisect' from Command Palette to try to identify the cause. -->
<!-- 📣 Issues caused by an extension need to be reported directly to the extension publisher. The 'Help > Report Issue' dialog can assist with this. -->
- VS Code Version: 1.65.2
- OS Version: Darwin x64 19.6.0

Steps to Reproduce:

1. Create a code snippet like this.

```json
{
	"TS -> Inject Service": {
		"scope": "typescript",
		"description": "Constructor Injection Pattern",
		"prefix": "@inject",
		"body": "@inject(${1/(.*)/I${1}Token/}) private readonly ${1/(.*)/${1:/camelcase}/}: I${1},$0"
	}
}
```

2. Using the snippet. 

![camelcase](https://user-images.githubusercontent.com/24731539/160342428-b0d6e71e-f472-4c34-8ce3-48b28ffc7e51.gif)

As I as concerned, the camelcase of `PathService` should be `pathService`. However, the result is `pathservice`. 

https://github.com/microsoft/vscode/blob/049b0e564b6bc1fcc07e9a39b727bca9836274f4/src/vs/editor/contrib/snippet/browser/snippetParser.ts#L404-L418

The implementation doesn't seems to tackle it well. 

I'd like to help if you could be so nice to give me a hint to fix the problem. 😃