Fix wrong bracket matching when parsing Vectors (#3837)

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## Fixes #3834
<!-- Add the relevant issue number after the "#" mentioned above (for ex: Fixes #1234) which will automatically close the issue once the PR is merged. -->

<!-- Add a brief overview here of the feature/bug & fix. -->
Fixed wrong bracket matching in `StringExtensions.ToVectorN(string)` and `StringExtensions.ToQuaternion(string)` methods.

## PR Type
What kind of change does this PR introduce?
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- Bugfix
<!-- - Feature -->
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
<!-- - Other... Please describe: -->


## What is the current behavior?
<!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->
Sample app crashes.


## What is the new behavior?
<!-- Describe how was this issue resolved or changed? -->
Sample app does not crash.


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- [ ] Tested code with current [supported SDKs](../readme.md#supported)
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## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.UI/Extensions/StringExtensions.cs

@@ -29,12 +29,7 @@ public static Vector2 ToVector2(this string text)
             if (text.Length > 0)
             {
                 // The format <x> or <x, y> is supported
-                if (text.Length >= 2 &&
-                    text[0] == '>' &&
-                    text[text.Length - 1] == '>')
-                {
-                    text = text.Substring(1, text.Length - 2);
-                }
+                text = Unbracket(text);
 
                 // Skip allocations when only a component is used
                 if (text.IndexOf(',') == -1)
@@ -78,12 +73,7 @@ public static Vector3 ToVector3(this string text)
         {
             if (text.Length > 0)
             {
-                if (text.Length >= 2 &&
-                    text[0] == '>' &&
-                    text[text.Length - 1] == '>')
-                {
-                    text = text.Substring(1, text.Length - 2);
-                }
+                text = Unbracket(text);
 
                 if (text.IndexOf(',') == -1)
                 {
@@ -127,12 +117,7 @@ public static Vector4 ToVector4(this string text)
         {
             if (text.Length > 0)
             {
-                if (text.Length >= 2 &&
-                    text[0] == '>' &&
-                    text[text.Length - 1] == '>')
-                {
-                    text = text.Substring(1, text.Length - 2);
-                }
+                text = Unbracket(text);
 
                 if (text.IndexOf(',') == -1)
                 {
@@ -176,12 +161,7 @@ public static Quaternion ToQuaternion(this string text)
         {
             if (text.Length > 0)
             {
-                if (text.Length >= 2 &&
-                    text[0] == '>' &&
-                    text[text.Length - 1] == '>')
-                {
-                    text = text.Substring(1, text.Length - 2);
-                }
+                text = Unbracket(text);
 
                 string[] values = text.Split(',');
 
@@ -201,5 +181,23 @@ public static Quaternion ToQuaternion(this string text)
 
             static Quaternion Throw(string text) => throw new FormatException($"Cannot convert \"{text}\" to {nameof(Quaternion)}. Use the format \"float, float, float, float\"");
         }
+
+        /// <summary>
+        /// Converts an angle bracketed <see cref="string"/> value to its unbracketed form (e.g. "&lt;float, float&gt;" to "float, float").
+        /// If the value is already unbracketed, this method will return the value unchanged.
+        /// </summary>
+        /// <param name="text">A bracketed <see cref="string"/> value.</param>
+        /// <returns>The unbracketed <see cref="string"/> value.</returns>
+        private static string Unbracket(string text)
+        {
+            if (text.Length >= 2 &&
+                text[0] == '<' &&
+                text[text.Length - 1] == '>')
+            {
+                text = text.Substring(1, text.Length - 2);
+            }
+
+            return text;
+        }
     }
 }