Trigger reparsing when files.encoding setting changes

[Colengms]

Fixes: #10892

This is a simple fix which will reindex the database if files.encoding changes. It's possible to do a more granular reparse of only those files that would have been impacted by the change. A related issue with that may be: microsoft/vscode#209503 (comment)

There is a native-side change as well.

[v-frankwang]

@Colengms @sean-mcmanus We went to verify the issue in the latest C++ extension 1.24.1 (pre-release) according to the following steps, is the gif showing the expected result?

If our validation steps are not correct, could you share our detailed validation steps?

Verification Steps:

1. Create a Demo folder in PC.
2. Open Demo with VSCode, then add a .cpp file and paste the following code:

#include <iostream>
#include <vector>
#include <string>
using namespace std;
int main()
{
 vector<string> msg {"Hello", "C++", "World", "from", "VS Code", "and the C++ extension!"};
    for (const string& word : msg)
    {
        cout << word << " ";
    }
    cout << endl;
}

4. Run the 'C/C++: Log Diagnostics' command in the command panel.
5. Observe the log info in the output panel, then get current database path.
6. Navigate to the DB path in PC.
7. Return to VSCode, then navigate to Settings UI, search for 'Files: Encoding'
8. Choose other windows encoding in the workspace tab.
9. Observe the DB file after returning to the .cpp file.

Verification Results: Changes to files.encoding trigger purge/reparse of files(.BROWSE.VC&.BROWSE.VC.DB-wal) in DB path