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/sksl/SkSLHCodeGenerator.cpp b/src/sksl/SkSLHCodeGenerator.cpp
index e9ab69d..92da59f 100644
--- a/src/sksl/SkSLHCodeGenerator.cpp
+++ b/src/sksl/SkSLHCodeGenerator.cpp
@@ -379,4 +379,4 @@
     return 0 == fErrors.errorCount();
 }
 
-} // namespace
+}  // namespace SkSL