Move VisitLiteral to decide what type of literal is being emitted by
checking the raw ASTValue type, instead of the internalized on-heap
value. This is required for concurrent bytecode generation.

As part of this change, the NUMBER AstValue constructor is modified to
try to convert numbers without a dot to SMIs where possible. This is to
maintain the behavior in NewNumber where such numbers are internalized as
SMIs, and ensures that we still emit LdaSmi bytecodes for these values
in the generated bytecode.

BUG=v8:5203

Review-Url: https://codereview.chromium.org/2152853002
Cr-Commit-Position: refs/heads/master@{#37931}