slide syntax should support `[import:1]`

Currently, support following patterns.

```
All: [import, hello-world.js](../src/hello-world.js)
1-2: [import:1-2, hello-world.js](../src/hello-world.js)
2-3: [import:2-3, hello-world.js](../src/hello-world.js)
2>=: [import:2-, hello-world.js](../src/hello-world.js)
<=3: [import:-3, hello-world.js](../src/hello-world.js)
```

We want to add following pattern:

```
1: [import:1, hello-world.js](../src/hello-world.js)
```

It is a alias of that

```
1: [import:1-1, hello-world.js](../src/hello-world.js)
```

Start by locating the parser or tests that handle the existing import range forms shown in the issue. Add coverage for [import:1] and verify that it behaves the same as [import:1-1], including the expected included line.

Written by the indexing model from the issue text.