SpringBoot Use pattern matching for instanceof where appropriate

Hi,

this PR uses pattern matching for instanceof where appropriate and closes #28181.

I explicitly didn't make use of it where its introduction would generate new rawtype warnings. And while I could add @SuppressWarnings("rawtypes") everywhere this didn't feel right. Typical example of this are Maps/Lists etc.:

if (item instanceof Map) {
    // do something (Map<String, Object>) item);
}
else if (item instanceof List) {
    // do something (List<Object>) item);
}

Let me know if I should make use of pattern matching in those cases as well and suppress the rawtype warnings.

Local tests were green, but I had no Docker running to not spend hours on waiting - so there might be some tests popping up in CI that I'll of course fix in case there is anything.

Cheers, Christoph

Comment From: dreis2211

Give me a minute @wilkinsona - I noticed a couple of missed opportunities to use pattern matching.

Comment From: wilkinsona

Gah. I missed that. Let me merge those too.

Comment From: dreis2211

My fault - my initial search missed stuff in multiple lines. Sorry