Move validation of text nesting into ReactDOMComponent (#26594)

Extract validateTextNesting from validateDOMNesting. We only need the
parent tag when validating text nodes. Then validate it in setProp.

DiffTrain build for [ac43bf6](ac43bf6)

Author: sebmarkbage

compiled/facebook-www/REVISION

@@ -1 +1 @@
-ca41adb8c1b256705f73d1fb657421a03dfad82c
+ac43bf6870a15566507477a4504f22160835c8d3

compiled/facebook-www/ReactART-prod.modern.js

@@ -9743,7 +9743,7 @@ var slice = Array.prototype.slice,
       return null;
     },
     bundleType: 0,
-    version: "18.3.0-www-modern-f0a7ed1e",
+    version: "18.3.0-www-modern-910e3a9f",
     rendererPackageName: "react-art"
   };
 var internals$jscomp$inline_1324 = {
@@ -9774,7 +9774,7 @@ var internals$jscomp$inline_1324 = {
   scheduleRoot: null,
   setRefreshHandler: null,
   getCurrentFiber: null,
-  reconcilerVersion: "18.3.0-www-modern-f0a7ed1e"
+  reconcilerVersion: "18.3.0-www-modern-910e3a9f"
 };
 if ("undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__) {
   var hook$jscomp$inline_1325 = __REACT_DEVTOOLS_GLOBAL_HOOK__;