Refine null-safety for additional `Assert` methods

[leikingo]

I saw the work being done to add @Contract annotations for null-safety analysis (#32475).

Having a look at the updates to org.springframework.util.Assert methods, I wonder why for example hasText was not annotated with @Contract(null,_ -> fail), although hasText would also throw an exception in case of null.

I'm often using only Assert.hasText for incoming @Nullable strings to ensure a non-null value afterwards. Unfortunately IntelliJ does not recognize this method correctly, like it does for Assert.notNull.

For now I need to add another notNull check in the code or use 'external contract annotations' in IntelliJ, which is quite cumbersome.

It would be great if @Contract annotations could be added to the remaining Assert methods as well to avoid this in the future hoping that they would then also be recognized by IntelliJ correctly).