JIT: lay out memory to group executable code together

[diegorusso]

When allocating memory to host JIT traces, we have the following layout:

• code
• data
• trampolines
• padding

We should group executable code together to improve icache locality. The new layout should be

• code
• trampolines
• data
• padding

Linked PRs

• gh-129231: group executable JIT code in memory #129232

[hugovk]

Triage: PR merged. Please re-open if there's more to do.