Support for Multiple FilterText Values in CompletionItem

[AlejandroJorba]

Issue Title:
Support for Multiple FilterText Values in CompletionItem

Issue Description:
Currently, CompletionItem only supports a single FilterText value. However, there are cases where multiple terms should match a single completion item.

Proposal:
Allow CompletionItem to accept an array of FilterText values instead of just one.

Languages applicable:
C#
VB.NET

Code Example (Current Limitation):

var item = new CompletionItem(
    displayText: "foreach",
    filterText: "for"  // Only a single filter text is allowed
);

🚨 Problem: If I want "foreach" to appear when the user types "for" or "loop", I can't do that today.

Proposed Solution:
Add support for multiple filter terms:

var item = new CompletionItem(
    displayText: "foreach",
    filterText: new[] { "for", "loop", "foreach" }  // Allow multiple filter texts
);

Use Case & Justification:
Helps match different user intents (e.g., "func" should match "function" and "fn").
Improves IDE experience by reducing unnecessary typing.