Activate method signature help upon selecting a completion

### Godot version

4.5.1.stable.official [f62fdbde1]

### VS Code version

1.105.1

### Godot Tools VS Code extension version

2.5.1

### System information

macOS Tahoe 26.0.1

### Problem statement

Method signature help does not appear immediately after selecting an autocomplete suggestion for a method. For example:

- Begin typing `my_m`
- Select `my_method` from the autocomplete list, and press return/tab
- _Editor adds remaining text and opening parenthesis: `my_method(`, but no signature info appears_
- Delete and retype `(` character
- _Signature info is activated_

### Proposed solution

Two potential solutions come to mind:

1. **Aligns with current extension behaviour**: Provide method signature assistance immediately upon selecting an autocompleted method (and continue to insert the opening parenthesis)
2. **Aligns with other VSCode LSP clients** (e.g. official Python and JS extensions): Preserve current activation behaviour for method signature assistance, but omit the opening parenthesis when completing a method name (leaving the user to type `(` and activate method help at that point)