Add format-specifier warnings to SkDebugf.

This CL fixes up many existing format-specifier violations in Skia.
Note that GCC has a warning for formatting nothing, so existing calls to
`SkDebugf("")` have been removed, or replaced with `SkDebugf("%s", "")`.
These were apparently meant to be used as a place to set a breakpoint.

Some of our clients also use SkDebug with bad format specifiers, so this
check is currently only enabled when SKIA_IMPLEMENTATION is true.

Change-Id: I8177a1298a624c6936adc24e0d8f481362a356d0
Bug: skia:12143
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/420902
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/docs/examples/IRect_height64.cpp b/docs/examples/IRect_height64.cpp
index 3fafc07..91aab2e 100644
--- a/docs/examples/IRect_height64.cpp
+++ b/docs/examples/IRect_height64.cpp
@@ -5,6 +5,6 @@
 REG_FIDDLE(IRect_height64, 256, 256, true, 0) {
 void draw(SkCanvas* canvas) {
     SkIRect large = { 1, -2147483647, 2, 2147483644 };
-    SkDebugf("height: %d height64: %lld\n", large.height(), large.height64());
+    SkDebugf("height: %d height64: %" PRId64 "\n", large.height(), large.height64());
 }
 }  // END FIDDLE