Fix clang-tidy warnings in aapt and aapt2.

* Add explicit keyword to conversion constructors.
* Add NOLINT(implicit) comments for implicit conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Id6d21961f313a1ad92b15a37fdaa5be9e8ab48e1
diff --git a/tools/aapt2/process/SymbolTable.cpp b/tools/aapt2/process/SymbolTable.cpp
index 6c506df..0c92718 100644
--- a/tools/aapt2/process/SymbolTable.cpp
+++ b/tools/aapt2/process/SymbolTable.cpp
@@ -63,7 +63,7 @@
     return nullptr;
 }
 
-const SymbolTable::Symbol* SymbolTable::findById(ResourceId id) {
+const SymbolTable::Symbol* SymbolTable::findById(const ResourceId& id) {
     if (const std::shared_ptr<Symbol>& s = mIdCache.get(id)) {
         return s.get();
     }