Nonbreaking performance tweaks (#17106)

* Avoid doing multiple lookups in dictionaries, avoid doing string interpolation & adding single char strings to a StringBuilder, made some private/internal classes & some private methods static when possible, use FrozenSet for InvalidFileNameChars

* Avoid some array + list allocations & async methods and made some private methods static

* Avoid double lookup of XML attribute (and double null check) & avoid an unneeded lookup before writing to a dictionary

* Avoid some double lookups

# Conflicts:
#	src/Umbraco.Core/Services/LocalizedTextService.cs

* Avoid double lookups

# Conflicts:
#	src/Umbraco.Core/Services/LocalizedTextService.cs

* Avoid double lookups

* List AsSpan, also to trigger a new build that hopefully goes through

* Avoid concatting strings when using writer & more static

* Updated CollectionBenchmarks to show that ToArray isn't always the fastest & Lists can be iterated nearly as fast as arrays (and that ToList is nearly as fast as ToArray on IReadOnlyLists in .NET 8)

* Fix rebase

* Use explicit types ❤️ (I thought it was the other way round...)

# Conflicts:
#	src/Umbraco.Core/Services/LocalizedTextService.cs

* Reduce number of lines in HtmlStringUtilities.Truncate to pass code quality analysis

* Avoid double lookups & allocating empty arrays

* Use native List Find instead of LINQ

src/Umbraco.Cms.Persistence.SqlServer/Services/SqlServerDatabaseProviderMetadata.cs

@@ -82,7 +82,7 @@ public class SqlServerDatabaseProviderMetadata : IDatabaseProviderMetadata
         return connectionString;
     }
 
-    private string HandleIntegratedAuthentication(string connectionString, DatabaseModel databaseModel)
+    private static string HandleIntegratedAuthentication(string connectionString, DatabaseModel databaseModel)
     {
         if (databaseModel.IntegratedAuth)
         {
@@ -96,7 +96,7 @@ public class SqlServerDatabaseProviderMetadata : IDatabaseProviderMetadata
         return connectionString;
     }
 
-    private string HandleTrustServerCertificate(string connectionString, DatabaseModel databaseModel)
+    private static string HandleTrustServerCertificate(string connectionString, DatabaseModel databaseModel)
     {
         if (databaseModel.TrustServerCertificate)
         {