[Bug]: IntelliSense suggests SQL keywords when entering a table alias

### Description

When aliasing a table in a SQL query, IntelliSense suggests and inserts an unrelated SQL keyword instead of respecting the alias the user is typing.

For example, while entering:

`SELECT * FROM Prices AS p`

if I type `p` and accept the completion with Enter, IntelliSense can insert `PARTIAL` instead of leaving the alias as `p`.

This appears to be incorrect context handling in IntelliSense. In an aliasing position, the editor should treat the input as an identifier/alias rather than prioritizing unrelated SQL keywords.

This issue is based on the Azure Data Studio issue https://github.com/microsoft/azuredatastudio/issues/25693.

### Steps to Reproduce

1. Open a SQL query editor connected to a database.
2. Type a query such as `SELECT * FROM Prices AS p`.
3. After typing `AS `, enter `p` for the alias.
4. Accept the IntelliSense suggestion with Enter.

### Expected Behavior

In an aliasing context:
- IntelliSense should not prioritize unrelated keywords such as `PARTIAL`
- accepting completion should preserve the intended alias identifier
- alias creation should behave as identifier entry, not keyword completion

### Actual Behavior

Typing `p` for the alias can cause IntelliSense to insert the keyword `PARTIAL` instead of keeping the alias as `p`, forcing the user to backtrack and correct the query.

### Affected Area

- Query editor
- Language service / IntelliSense behavior

### Environment Information

- VS Code Version: [fill in]
- MSSQL Extension Version: [fill in]
- Operating System: Windows
- Connection Type: SQL Server

Start in the query editor's language service and IntelliSense completion handling, then reproduce the issue with `SELECT * FROM Prices AS p` after typing `AS `. Trace why `PARTIAL` is selected for the alias prefix; done means accepting completion preserves `p` rather than inserting an unrelated keyword.

Written by the indexing model from the issue text.