LibJS/Bytecode: Add peephole optimization pass and fuse compare+jump

This patch adds a new "Peephole" pass for performing small, local
optimizations to bytecode.

We also introduce the first such optimization, fusing a sequence of
some comparison instruction FooCompare followed by a JumpIf into a
new set of JumpFooCompare instructions.

This gives a ~50% speed-up on the following microbenchmark:

    for (let i = 0; i < 10_000_000; ++i) {
    }

But more traditional benchmarks see a pretty sizable speed-up as well,
for example 15% on Kraken/ai-astar.js and 16% on Kraken/audio-dft.js :^)

Userland/Libraries/LibJS/Bytecode/Instruction.h

@@ -69,6 +69,14 @@
     O(IteratorToArray)                 \
     O(Jump)                            \
     O(JumpIf)                          \
+    O(JumpGreaterThan)                 \
+    O(JumpGreaterThanEquals)           \
+    O(JumpLessThan)                    \
+    O(JumpLessThanEquals)              \
+    O(JumpLooselyEquals)               \
+    O(JumpLooselyInequals)             \
+    O(JumpStrictlyEquals)              \
+    O(JumpStrictlyInequals)            \
     O(JumpNullish)                     \
     O(JumpUndefined)                   \
     O(LeaveLexicalEnvironment)         \