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/tools/skui/ModifierKey.h b/tools/skui/ModifierKey.h
index ffb358c..ffb9500 100644
--- a/tools/skui/ModifierKey.h
+++ b/tools/skui/ModifierKey.h
@@ -14,9 +14,9 @@
     kCommand    = 1 << 3,
     kFirstPress = 1 << 4,
 };
-}
+}  // namespace skui
 
 namespace sknonstd {
 template <> struct is_bitmask_enum<skui::ModifierKey> : std::true_type {};
-}
+}  // namespace sknonstd
 #endif  // skui_modifierkey_defined