Add .git-blame-ignore-revs file (#19956)

Include a couple of obvious reformatting-only revisions to get it
started and test is out.

Author: sbc100

.git-blame-ignore-revs

@@ -0,0 +1,12 @@
+# This file contains a list of commits that are not likely what you
+# are looking for in a blame, such as mass reformatting or renaming.
+# You can set this file as a default ignore file for blame by running
+# the following command.
+#
+# $ git config blame.ignoreRevsFile .git-blame-ignore-revs
+
+# Remove tabs and fix formatting in test/sse/.  NFC (#18245)
+3cd47cff5da467ae7ca2a29490d8b04af897023f
+
+# [embind docs] Reformat and cleanup whitespace.
+9b1a5910c4f31cff4949541a42ac956ba45e4701