Support for Multiple FilterText Values in CompletionItem

**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.