feat: add built-in FileSystem

[nodece]

Motivation

The casbin can only use the Node.js FileSystem module, when users want to use the custom FileSystem, the casbin doesn't support that.

Modification

• Define the FileSystem interface, and add default implement
• Add FileSystem to Enforce, Model, Config, and FileAdapter

[casbin-bot]

@Zxilly @Shivansh-yadav13 please review

[Zxilly]

To keep forward-compatibility, maybe legacy node fs can be used as an default implementation?
To avoid bundle error, use require.

if (typeof global === 'object') {
    const fs = __non_webpack_require__('fs');
    const defaultFileSystem = {
        readFileSync(path, encoding) {
            return fs.readFileSync(path, encoding);
        },
        writeFileSync(path, text, encoding) {
            return fs.writeFileSync(path, text, encoding);
        },
    };
    setDefaultFileSystem(defaultFileSystem);
}

This is a webpack specific implementation, for possible other bundlers we need more work.

Another possible solution is

const fs = eval('require("fs")')

[nodece]

Ping @Zxilly

[nodece]

Right now, there are no breaking changes.

[Zxilly]

lgtm

[github-actions]

🎉 This PR is included in version 5.24.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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