Enable ClangTidy check llvm-namespace-comment.

This fixes a large number of SkSL namespaces which were labeled as if
they were anonymous, and also a handful of other mislabeled namespaces.
Missing namespace-end comments have been added throughout.
A number of diffs are just indentation-related (adjusting 1- or 3-
space indents to 2-space).

Change-Id: I6c62052a0d3aea4ae12ca07e0c2a8587b2fce4ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/308503
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
diff --git a/src/utils/SkMultiPictureDocument.cpp b/src/utils/SkMultiPictureDocument.cpp
index 8a47be1..c78ed59 100644
--- a/src/utils/SkMultiPictureDocument.cpp
+++ b/src/utils/SkMultiPictureDocument.cpp
@@ -94,7 +94,7 @@
         fSizes.reset();
     }
 };
-}
+}  // namespace
 
 sk_sp<SkDocument> SkMakeMultiPictureDocument(SkWStream* wStream, const SkSerialProcs* procs) {
     return sk_make_sp<MultiPictureDocument>(wStream, procs);