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/.clang-tidy b/.clang-tidy
index f5e2188..a9a2c42 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1 +1,4 @@
-Checks: '-*,bugprone-use-after-move,bugprone-unused-raii,bugprone-undelegated-constructor,bugprone-argument-comment,performance-for-range-copy,bugprone-bool-pointer-implicit-conversion,readability-redundant-preprocessor,misc-definitions-in-headers,modernize-make-unique,google-build-namespaces'
+Checks: '-*,bugprone-use-after-move,bugprone-unused-raii,bugprone-undelegated-constructor,bugprone-argument-comment,performance-for-range-copy,bugprone-bool-pointer-implicit-conversion,readability-redundant-preprocessor,misc-definitions-in-headers,modernize-make-unique,llvm-namespace-comment,google-build-namespaces'
+CheckOptions:
+  - key:             llvm-namespace-comment.SpacesBeforeComments
+    value:           2