Restore support of exact match property

This commit fixes a regression in property placeholder resolution where
the original key was no longer considered for an exact match before
processing the placeholder itself.

By default, property resolution uses ':' as the separator between the
key and the fallback value.

Consider a request to resolve ${prefix://service}. Previously,
placeholder resolution would first attempt to resolve the raw text, that
is 'prefix://service', before attempting to resolve the 'prefix' key and
then use '//service' if the key did not resolve.

This commit restores that behaviour purely for backward compatible
reason.

Closes gh-34124

spring-core/src/main/java/org/springframework/util/PlaceholderParser.java

@@ -519,7 +519,7 @@ final class PlaceholderParser {
 
 		@Override
 		public String resolve(PartResolutionContext resolutionContext) {
-			String value = resolveRecursively(resolutionContext, this.key);
+			String value = resolveRecursively(resolutionContext);
 			if (value != null) {
 				return value;
 			}
@@ -528,6 +528,17 @@ final class PlaceholderParser {
 			}
 			return resolutionContext.handleUnresolvablePlaceholder(this.key, text());
 		}
+
+		@Nullable
+		private String resolveRecursively(PartResolutionContext resolutionContext) {
+			if (!this.text().equals(this.key)) {
+				String value = resolveRecursively(resolutionContext, this.text());
+				if (value != null) {
+					return value;
+				}
+			}
+			return resolveRecursively(resolutionContext, this.key);
+		}
 	}