Strong api string localizers generator using incremental generator

[jirikanda]

• No longer generates marker classes (no garbage in IntelliSense 💪).
• No longer uses DelegatingStringLocalizer (Havit.Extensions.Localization now serves no purpose).
• Generates neutral value comments in the code.
• No longer searches for or uses the ResourceServiceCollectionInstaller partial class (the generator now produces its own static class).
• Includes a unit test.

• Localizers no longer implement IStringLocalizer<>, they implement only IStringLocalizer (therefore, no marker class is needed).
• Generators cannot detect RESX files unless explicitly mentioned in the .csproj file.
• Generates a warning when no RESX file is found, including a hint on how to modify the .csproj file (can check if this can be implemented using a code fix).
• Uses a clone of HttpUtilityExt for human-readable, culture-specific character HTML encoding (e.g., "á" remains "á" and is not converted to an HTML entity).