[Java] Avoid ambiguous references for date and time classes (#18416) (#20230)

Author: jbrugge

modules/openapi-generator/src/main/resources/Java/JSON.mustache

@@ -31,9 +31,11 @@ import java.lang.reflect.Type;
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.ParsePosition;
+{{#jsr310}}
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.format.DateTimeFormatter;
+{{/jsr310}}
 import java.util.Date;
 import java.util.Locale;
 import java.util.Map;

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/ApiClient.mustache

@@ -47,9 +47,11 @@ import java.security.cert.CertificateException;
 import java.security.cert.CertificateFactory;
 import java.security.cert.X509Certificate;
 import java.text.DateFormat;
+{{#jsr310}}
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.format.DateTimeFormatter;
+{{/jsr310}}
 import java.util.*;
 import java.util.Map.Entry;
 import java.util.concurrent.TimeUnit;

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache

@@ -28,9 +28,11 @@ import java.lang.reflect.Type;
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.ParsePosition;
+{{#jsr310}}
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.format.DateTimeFormatter;
+{{/jsr310}}
 import java.util.Date;
 import java.util.Locale;
 import java.util.Map;

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/ApiClient.mustache

@@ -46,7 +46,9 @@ import java.io.IOException;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Type;
 import java.text.DateFormat;
+{{#jsr310}}
 import java.time.format.DateTimeFormatter;
+{{/jsr310}}
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.HashMap;

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/JSON.mustache

@@ -30,9 +30,11 @@ import java.lang.reflect.Type;
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.ParsePosition;
+{{#jsr310}}
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.format.DateTimeFormatter;
+{{/jsr310}}
 import java.util.Date;
 import java.util.Locale;
 import java.util.Map;