Implement asterisk expansion feature with settings and UI integration

[Blake-goofy]

Implemented John's suggested idea from #103

Summary

Adds configurable SELECT * expansion from the query editor. When enabled, placing the cursor immediately after * and pressing the configured trigger key replaces the asterisk with the resolved column list.

Capabilities

• Configurable trigger key in Settings: Tab, Enter, or Shift+Enter.
• Coexists with snippet expansion; snippets get first chance on shared trigger keys.
• Supports plain SELECT * FROM table.
• Supports SELECT existing_column, * FROM table.
• Supports temp tables declared earlier in the editor with CREATE TABLE #temp (...).
• Supports joined tables for SELECT *.
• Supports prior simple SELECT INTO #temp statements when the output columns can be inferred from the select list or resolved metadata.
• Qualifies duplicate column names using:
  -- table alias when present, like t.[HireDate]
  -- table name when no alias exists, like [#Employees].[HireDate]
• Supports alias.* by expanding only that table’s columns.
• Falls back to metadata discovery when direct table-column lookup is not available.

Notes

• Opt-in only; not enabled by default.
• Requires a live SQL Server connection for metadata lookup.
• Table variables declared earlier in the same batch are resolved directly from their DECLARE @table TABLE definition.
• CTEs are resolved directly for explicit column lists, simple projected columns, aliases, chained CTEs, and CTE SELECT * over resolvable sources.
• Asterisk expansion inside CTE bodies is supported for resolvable sources.
• Derived tables are still best-effort and may require metadata fallback.
• Only replays prior CREATE TABLE #temp statements, not arbitrary previous SQL.
• Does not support SELECT INTO shapes that depend on dynamic SQL, stored procedures, conditional execution, or later
• Does not account for later ALTER TABLE #temp changes.
• Complex query shapes may fall back to SET FMTONLY ON, which is deprecated and imperfect.
• FMTONLY fallback is only used for the outer selected statement, not for asterisk expansion inside CTE bodies.
• Does not use SSMS IntelliSense internals; it relies on ScriptDom plus SQL Server metadata.
• If metadata cannot be resolved, expansion fails closed and the original key behavior continues.

Open questions

• I put the settings in Code Snippets sections; should asterisk expansion have its own section?
• Should there be more settings like: always include alias / table name, etc. ?

[alex-bochkov]

@Blake-goofy Great job getting this done. Let me take a look at it this week.

[alex-bochkov]

@Blake-goofy A few things:

• My first instinct was to press Ctrl+Space after * to trigger the feature. Could you please add this option?
• The Replace... checkbox in settings should be disabled when snippets are not enabled. The user must enable both options if they want the * expansion.
• Below are a few examples where the table alias is not added correctly.

Overall, it looks great!

[Blake-goofy]

@alex-bochkov I see the issue with the first example. That is a scenario I did not consider; good catch.
What is the issue with the second example? Are you expecting the alias to always be applied? Right now it only uses alias / table name to avoid ambiguity or when the user writes alias before the *.

[alex-bochkov]

When a query references only a single table, it's fine to list columns without a table alias. However, once two or more tables are involved, we should qualify all columns with their table aliases. This is generally considered a best practice and makes the code easier to read and maintain.