Specialize parsing of blocks of the same elements

[w0rm]

Having read the "Use specialization" section of https://romgrk.com/posts/optimizing-javascript#9-use-specialization I got another idea for performance optimization.

Oftentimes, the lines that define vertices, normals, uvs and faces are grouped. This means that if the parser encounters a line that defines a vertex (starting with v), it could switch into the mode of parsing only vertices until it sees something else. In this mode, each next line only needs to be checked if it starts with v, instead of being considered for any other possibility.

This made the parser 24% faster in Safari

And 6% faster in Chrome