Change default diff whitespace to IGNORE_LEADING_AND_TRAILING

The current default option is IGNORE_ALL, which thinks "abc" == "a b c".
This doesn't make sense for most of the programming languages.

IGNORE_LEADING_AND_TRAILING is the option that is sane and most close to
IGNORE_ALL.

An example is [1], comparing the output between:

curl 'https://go-review.googlesource.com/changes/20820/revisions/1/files/src%2Fcmd%2Fvet%2Fmain.go/diff'

and

curl 'https://go-review.googlesource.com/changes/20820/revisions/1/files/src%2Fcmd%2Fvet%2Fmain.go/diff?whitespace=IGNORE_LEADING_AND_TRAILING'

[1] https://go-review.googlesource.com/#/c/20820/1/src/cmd/vet/main.go

Change-Id: Ie56c487d077b65997716e0a184e414235b7a3dac
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/change/GetDiff.java b/gerrit-server/src/main/java/com/google/gerrit/server/change/GetDiff.java
index 1728c35..5cf5895 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/change/GetDiff.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/change/GetDiff.java
@@ -130,7 +130,7 @@
     } else if (ignoreWhitespace != null) {
       prefs.ignoreWhitespace = ignoreWhitespace.whitespace;
     } else {
-      prefs.ignoreWhitespace = Whitespace.IGNORE_ALL;
+      prefs.ignoreWhitespace = Whitespace.IGNORE_LEADING_AND_TRAILING;
     }
     prefs.context = context;
     prefs.intralineDifference = intraline;