SymbolicTypedArray#length is wrong in WebGL Backend

[Kiikurage]

In WebGL backend, buffer is implemented by using WebGL Texture and the texture size is not always same as actual buffer size (larger than actual).

To fix this problem,

• In transpiler backend, output actual buffer size information in descriptor
• In descriptor runner, load and set the information into each buffer instance.

[lygstate]

I also see this problem