Centralize Java thread detection and type-safe thread state handling

[zhengyu123]

What does this PR do?:
Centralize Java thread detection and improve thread state handling

Motivation:
Consolidate and cleanup code for consistence, maintainability and readability.

Additional Notes:

Consolidate Java thread detection
Java thread detection was scattered across VMThread instance methods, each calling cachedIsJavaThread() independently. Thread state comparisons used magic integers throughout (>= 4, < 12, ==
8, == 10, == 11), making the code fragile and hard to audit.

Centralized VMThread::isJavaThread(VMThread)*
Replaces the old cachedIsJavaThread() pattern with a single static method that:

• Returns false immediately for nullptr (native/JNI threads outside the JVM)
• Consults the ProfiledThread cache for previously determined results (TYPE_JAVA_THREAD / TYPE_NOT_JAVA_THREAD)
• Falls back to vtable comparison (hasJavaThreadVtable()) for uncached threads, then stores the result

JVMJavaThreadState enum
Names the previously magic thread state integers with HotSpot-matching constants (_thread_in_Java, _thread_blocked, _thread_blocked_trans, etc.). A new convertJvmExecutionState() switch maps
them to ExecutionMode in a type-safe, exhaustive way.

Safer vtable reads
hasJavaThreadVtable() now uses SafeAccess::load() for the vtable slot comparison, guarding against unmapped memory access.

Cleaner ProfiledThread flag API
Thread type is stored as a 2-bit field in _misc_flags via setJavaThread(bool) / threadType(), replacing the ad-hoc flag manipulation in the old code.

How to test the change?:

• Passed CI tests
• Passed stress tests

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.
• JIRA: PROF-14160

Unsure? Have a question? Request a review!

[dd-octo-sts]

CI Test Results

Run: #24268357704 | Commit: 2552224 | Duration: 21m 30s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

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Updated: 2026-04-11 00:22:37 UTC