Don't follow the swiftly symlink when determining in use toolchain

When swiftly is installed via Homebrew it is added to the path at a
location like `/opt/homebrew/bin/swiftly`, which is a symlink to the
brew cellar located at `/opt/homebrew/bin/Cellar/swiftly/1.1.0/bin/`

When printing the in use toolchain location with `swiftly use
--print-location` we were launching swiftly with the realpath of the
symlink, which caused Swiftly to print the "swiftly is unlinked" warning
message before printing the toolchain location.

The extension went on to take this message and parse it as a path,
causing the extension activation to hang.

Instead of using this realpath when invoking swiftly to get the
toolchain path, if we determine the use is using swiftly just invoke it
normally using `swiftly` instead of using the full path.

Issue: #1966

Author: plemarquand

src/toolchain/toolchain.ts

@@ -571,7 +571,7 @@ export class SwiftToolchain {
 
             if (path.basename(realSwift) === "swiftly") {
                 try {
-                    const inUse = await Swiftly.inUseLocation(realSwift, cwd);
+                    const inUse = await Swiftly.inUseLocation("swiftly", cwd);
                     if (inUse) {
                         realSwift = path.join(inUse, "usr", "bin", "swift");
                         isSwiftlyManaged = true;