+ Add bytecodes for conditional and unconditional jumps.
+ Add bytecodes for test/compare operations.
+ Expose jumps in bytecode-array-builder and add BytecodeLabel class for
  identifying jump targets.
+ Add support for if..then...else in the bytecode-generator.
+ Implement jump bytecodes in the interpreter. Test/compare operations
  dependent on runtime call for comparisons.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1343363002

Cr-Commit-Position: refs/heads/master@{#30918}