Bug 1297306 - part5:create enum constructors for EnumTable. r=baku

Enable nsAttrValue::EnumTable to be initialized with enum. So, we could get rid
of the castings in EnumTable. Fix EnumTable initialization comment.

For those untyped enumerations, declare them with uint8_t, as to other typed
enumerations with type size larger than int16_t, force casting to int16_t.

Use {nullptr,0} instead of {0} to represent the last entry.

MozReview-Commit-ID: 7Dma3Apkmxj

dom/html/HTMLInputElement.cpp

@@ -178,7 +178,7 @@ static const nsAttrValue::EnumTable kInputTypeTable[] = {
   { "time", NS_FORM_INPUT_TIME },
   { "url", NS_FORM_INPUT_URL },
   { "week", NS_FORM_INPUT_WEEK },
-  { 0 }
+  { nullptr, 0 }
 };
 
 // Default type is 'text'.
@@ -200,7 +200,7 @@ static const nsAttrValue::EnumTable kInputInputmodeTable[] = {
   { "lowercase", NS_INPUT_INPUTMODE_LOWERCASE },
   { "titlecase", NS_INPUT_INPUTMODE_TITLECASE },
   { "autocapitalized", NS_INPUT_INPUTMODE_AUTOCAPITALIZED },
-  { 0 }
+  { nullptr, 0 }
 };
 
 // Default inputmode value is "auto".