Bug 1642940 - Factor out data/elem segment implementation limits. r=lth

Data and element segment decoding used the initial memory/table limit values
which will be removed in a later commit, this commit gives data/elem segments
their own implementation defined limit to prevent interference.

Differential Revision: https://phabricator.services.mozilla.com/D80137

js/src/wasm/WasmConstants.h

@@ -849,7 +849,9 @@ static const unsigned MaxImports = 100000;
 static const unsigned MaxExports = 100000;
 static const unsigned MaxGlobals = 1000000;
 static const unsigned MaxDataSegments = 100000;
+static const unsigned MaxDataSegmentLengthPages = 16384;
 static const unsigned MaxElemSegments = 10000000;
+static const unsigned MaxElemSegmentLength = 10000000;
 static const unsigned MaxTableLength = 10000000;
 static const unsigned MaxLocals = 50000;
 static const unsigned MaxParams = 1000;

js/src/wasm/WasmValidate.cpp

@@ -2735,7 +2735,7 @@ static bool DecodeElemSection(Decoder& d, ModuleEnvironment* env) {
       return d.fail("expected segment size");
     }
 
-    if (numElems > MaxTableInitialLength) {
+    if (numElems > MaxElemSegmentLength) {
       return d.fail("too many table elements");
     }
 
@@ -3052,7 +3052,7 @@ static bool DecodeDataSection(Decoder& d, ModuleEnvironment* env) {
       return d.fail("expected segment size");
     }
 
-    if (seg.length > MaxMemoryInitialPages * PageSize) {
+    if (seg.length > MaxDataSegmentLengthPages * PageSize) {
       return d.fail("segment size too big");
     }