[JS/TS] Rewrite flexbuffers JS to TS (#6148)

* Partial TS rewrite

* Completed port but bugs remain

* Expose builder function

* Break out and fix stack-value and formatting

ts/flexbuffers/value-type-util.ts

@@ -0,0 +1,64 @@
+import { ValueType } from './value-type'
+
+export function isInline(value: ValueType): boolean {
+  return value === ValueType.BOOL
+    || value <= ValueType.FLOAT;
+}
+
+export function isNumber(value: ValueType): boolean {
+  return value >= ValueType.INT
+    && value <= ValueType.FLOAT;
+}
+
+export function isIndirectNumber(value: ValueType): boolean {
+  return value >= ValueType.INDIRECT_INT
+    && value <= ValueType.INDIRECT_FLOAT;
+}
+
+export function isTypedVectorElement(value: ValueType): boolean {
+  return value === ValueType.BOOL
+    || (value >= ValueType.INT
+      && value <= ValueType.STRING);
+}
+
+export function isTypedVector(value: ValueType): boolean {
+  return value === ValueType.VECTOR_BOOL
+    || (value >= ValueType.VECTOR_INT
+      && value <= ValueType.VECTOR_STRING_DEPRECATED);
+}
+
+export function isFixedTypedVector(value: ValueType): boolean {
+  return value >= ValueType.VECTOR_INT2
+    && value <= ValueType.VECTOR_FLOAT4;
+}
+
+export function isAVector(value: ValueType): boolean {
+  return isTypedVector(value)
+    || isFixedTypedVector(value)
+    || value === ValueType.VECTOR;
+}
+
+export function toTypedVector(valueType: ValueType, length: number): ValueType {
+  if (length === 0) return valueType - ValueType.INT + ValueType.VECTOR_INT;
+  if (length === 2) return valueType - ValueType.INT + ValueType.VECTOR_INT2;
+  if (length === 3) return valueType - ValueType.INT + ValueType.VECTOR_INT3;
+  if (length === 4) return valueType - ValueType.INT + ValueType.VECTOR_INT4;
+  throw "Unexpected length " + length;
+}
+
+export function typedVectorElementType(valueType: ValueType): ValueType {
+  return valueType - ValueType.VECTOR_INT + ValueType.INT;
+}
+
+export function fixedTypedVectorElementType(valueType: ValueType): ValueType {
+  return ((valueType - ValueType.VECTOR_INT2) % 3) + ValueType.INT;
+}
+
+export function fixedTypedVectorElementSize(valueType: ValueType): ValueType {
+  // The x / y >> 0 trick is to have an int division. Suppose to be faster than Math.floor()
+  return (((valueType - ValueType.VECTOR_INT2) / 3) >> 0) + 2;
+}
+
+export function packedType(valueType: ValueType, bitWidth: number): ValueType {
+  return bitWidth | (valueType << 2);
+}