Single-char-prefix snippet suggestion is not case sensitive

<!-- ⚠️⚠️ Do Not Delete This! bug_report_template ⚠️⚠️ --> <!-- 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. --> <!-- 🧪 Test using the latest Insiders build to see if your issue has already been fixed: https://code.visualstudio.com/insiders/ --> <!-- 💡 Instead of creating your report here, use 'Report Issue' from the 'Help' menu in VS Code to pre-fill useful information. --> <!-- 🔧 Launch with `code --disable-extensions` to check. --> Does this issue occur when all extensions are disabled?: Yes <!-- 🪓 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:1.63.2 - OS Version:Windows 10 Almost same as [issue 8070](https://github.com/microsoft/vscode/issues/8070), in which the reported bug has been fixed. However, if the snippet prefix is a single char, suggestion remains case insensitive. For example, if I define a `Result` snippet with prefix `Re` and `return` snippet with prefix `re`, while typing `re`, `return` will be the first suggestion. But if the prefix is `R` and `r` respectively, `Result` will be on top while typing `r`.