[nativeaot] fix Java string escaping and logging in environment variables support code (#10771)

This PR applies review feedback from the backport PR #10768 to the main branch, addressing three improvements to the NativeAOT environment variable handling:

**Changes:**
- Fixed Java string escaping in `EnvironmentBuilder.cs` to properly escape backslashes before quotes, preventing invalid Java string literals
- Added missing `$` prefix for string interpolation in a test assertion message in `EnvironmentHelper.cs`
- Enhanced error logging in `NativeAotEnvironmentVars.java` to include exception details when environment variable setting fails

Author: Copilot

src/Xamarin.Android.Build.Tasks/Resources/NativeAotEnvironmentVars.java

@@ -32,7 +32,7 @@ public static void Initialize ()
 				Os.setenv (envNames[i], envValues[i], true /* overwrite */);
 			}
 		} catch (ErrnoException e) {
-			Log.e (TAG, "Failed to set environment variables");
+			Log.e (TAG, "Failed to set environment variables", e);
 		}
 	}
 }

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/EnvironmentHelper.cs

@@ -842,7 +842,7 @@ public static Dictionary<string, string> ReadNativeAotEnvironmentVariables (stri
 				}
 			}
 
-			Assert.AreEqual (names.Count, values.Count, "Environment variable name and value arrays aren't of the same size in '{javaSourcePath}'");
+			Assert.AreEqual (names.Count, values.Count, $"Environment variable name and value arrays aren't of the same size in '{javaSourcePath}'");
 			for (int i = 0; i < names.Count; i++) {
 				ret.Add (names[i], values[i]);
 			}

src/Xamarin.Android.Build.Tasks/Utilities/EnvironmentBuilder.cs

@@ -108,5 +108,5 @@ public void AddMonoGcParams (bool enableSgenConcurrent)
 		AddEnvironmentVariable ("MONO_GC_PARAMS", enableSgenConcurrent ? "major=marksweep-conc" : "major=marksweep");
 	}
 
-	static string ValidAssemblerString (string s) => s.Replace ("\"", "\\\"");
+	static string ValidAssemblerString (string s) => s.Replace ("\\", "\\\\").Replace ("\"", "\\\"");
 }