Migrate from android::String isEmpty to empty

This empty method is different from the old one - it aligns with
std::string definition.

Bug: 295394788
Test: make checkbuild
Change-Id: Id74502de0e51182aa9629db8dc70739be4483d12
Merged-In: Id74502de0e51182aa9629db8dc70739be4483d12
diff --git a/libs/input/PropertyMap.cpp b/libs/input/PropertyMap.cpp
index fc020ca..9f72c86 100644
--- a/libs/input/PropertyMap.cpp
+++ b/libs/input/PropertyMap.cpp
@@ -155,7 +155,7 @@
 
         if (!mTokenizer->isEol() && mTokenizer->peekChar() != '#') {
             String8 keyToken = mTokenizer->nextToken(WHITESPACE_OR_PROPERTY_DELIMITER);
-            if (keyToken.isEmpty()) {
+            if (keyToken.empty()) {
                 ALOGE("%s: Expected non-empty property key.", mTokenizer->getLocation().c_str());
                 return BAD_VALUE;
             }