Fixes vscode path installed via snap (#136997)

Fixes the #136996
Readresses the #54358

Before:
```sh
[✓] VS Code (version unknown)
    • VS Code at /snap/code/current
    • Flutter extension version 3.74.0
    ✗ Unable to determine VS Code version.
```

After:
```sh
[✓] VS Code (version 1.83.1)
    • VS Code at /snap/code/current/usr/share/code
    • Flutter extension version 3.74.0
```

*List which issues are fixed by this PR. You must list at least one
issue.*

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there for submitting PRs.
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responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

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packages/flutter_tools/lib/src/vscode/vscode.dart

@@ -238,7 +238,7 @@ class VsCode {
 
   // Linux:
   //   /usr/share/code/bin/code
-  //   /snap/code/current
+  //   /snap/code/current/usr/share/code
   //   /usr/share/code-insiders/bin/code-insiders
   // Linux Extensions:
   //   $HOME/.vscode/extensions
@@ -246,7 +246,7 @@ class VsCode {
   static List<VsCode> _installedLinux(FileSystem fileSystem, Platform platform) {
     return _findInstalled(<VsCodeInstallLocation>[
       const VsCodeInstallLocation('/usr/share/code', '.vscode'),
-      const VsCodeInstallLocation('/snap/code/current', '.vscode'),
+      const VsCodeInstallLocation('/snap/code/current/usr/share/code', '.vscode'),
       const VsCodeInstallLocation(
         '/usr/share/code-insiders',
         '.vscode-insiders',

packages/flutter_tools/test/general.shard/vscode/vscode_test.dart

@@ -45,7 +45,7 @@ void main() {
     const String home = '/home/me';
     final Platform platform = FakePlatform(environment: <String, String>{'HOME': home});
 
-    fileSystem.directory(fileSystem.path.join('/snap/code/current/', '.vscode')).createSync(recursive: true);
+    fileSystem.directory(fileSystem.path.join('/snap/code/current/usr/share/code', '.vscode')).createSync(recursive: true);
 
     final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[]);