Prevent raw Unicode control codes from showing on software keyboard applet. (#3845)

* Revert "Add support for releasing a semaphore to DmaClass (#2926)"

This reverts commit 521a07e612.

* Revert "Revert "Add support for releasing a semaphore to DmaClass (#2926)""

This reverts commit ec8a5fd053.

* Strip non-visible control codes from strings before they are sent to the software keyboard to prevent ugly unicode blocks from being shown on the UI.

* remove debugging junk

* Initialize stringbuilder capacity at the start to prevent resizing (a tiny tiny microoptimization)

* Update remarks documentation. Remove unneeded imports.

* Removing a test that's actually just redundant

Co-authored-by: Logan Stromberg <lostromb@microsoft.com>

Ryujinx.Tests/HLE/SoftwareKeyboardTests.cs

@@ -0,0 +1,71 @@
+using NUnit.Framework;
+using Ryujinx.HLE.HOS.Applets;
+using System.Text;
+
+namespace Ryujinx.Tests.HLE
+{
+    public class SoftwareKeyboardTests
+    {
+        [Test]
+        public void StripUnicodeControlCodes_NullInput()
+        {
+            Assert.IsNull(SoftwareKeyboardApplet.StripUnicodeControlCodes(null));
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_EmptyInput()
+        {
+            Assert.AreEqual(string.Empty, SoftwareKeyboardApplet.StripUnicodeControlCodes(string.Empty));
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_Passthrough()
+        {
+            string[] prompts = new string[]
+            {
+                "Please name him.",
+                "Name her, too.",
+                "Name your friend.",
+                "Name another friend.",
+                "Name your pet.",
+                "Favorite homemade food?",
+                "What’s your favorite thing?",
+                "Are you sure?",
+            };
+
+            foreach (string prompt in prompts)
+            {
+                Assert.AreEqual(prompt, SoftwareKeyboardApplet.StripUnicodeControlCodes(prompt));
+            }
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_StripsNewlines()
+        {
+            Assert.AreEqual("I am very tall", SoftwareKeyboardApplet.StripUnicodeControlCodes("I \r\nam \r\nvery \r\ntall"));
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_StripsDeviceControls()
+        {
+            // 0x13 is control code DC3 used by some games
+            string specialInput = Encoding.UTF8.GetString(new byte[] { 0x13, 0x53, 0x68, 0x69, 0x6E, 0x65, 0x13 });
+            Assert.AreEqual("Shine", SoftwareKeyboardApplet.StripUnicodeControlCodes(specialInput));
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_StripsToEmptyString()
+        {
+            string specialInput = Encoding.UTF8.GetString(new byte[] { 17, 18, 19, 20 }); // DC1 - DC4 special codes
+            Assert.AreEqual(string.Empty, SoftwareKeyboardApplet.StripUnicodeControlCodes(specialInput));
+        }
+
+        [Test]
+        public void StripUnicodeControlCodes_PreservesMultiCodePoints()
+        {
+            // Turtles are a good example of multi-codepoint Unicode chars
+            string specialInput = "♀ 🐢 🐢 ♂ ";
+            Assert.AreEqual(specialInput, SoftwareKeyboardApplet.StripUnicodeControlCodes(specialInput));
+        }
+    }
+}