Avoid use of 'sanity' and 'sanity check' in the code base (#3585)

In line with:

  https://source.android.com/setup/contribute/respectful-code

this change uses the terms 'coherence' and 'coherence check' where
'sanity' and 'sanity check' were previously used.

test/binary_parse_test.cpp

@@ -92,7 +92,7 @@ std::ostream& operator<<(std::ostream& os, const ParsedInstruction& inst) {
   return os;
 }
 
-// Sanity check for the equality operator on ParsedInstruction.
+// Coherence check for the equality operator on ParsedInstruction.
 TEST(ParsedInstruction, ZeroInitializedAreEqual) {
   spv_parsed_instruction_t pi = {};
   ParsedInstruction a(pi);