What does this PR do?:
Hardens ElfParser's parsing of the PT_DYNAMIC section and related virtual-address-relative structures (DT_HASH, DT_GNU_HASH, DT_SYMTAB/DT_STRTAB, .rela.plt/.rela.dyn relocation tables, the SFrame/eh_frame_hdr unwind sections) against corrupted or malformed ELF metadata found in a live-mapped shared library.

• Adds ElfParser::inLiveImage() / liveSegmentEnd() / liveImageEnd(), a bounds-checking layer for pointers derived from at()/dyn_ptr() (virtual addresses in live process memory), parallel to the existing inImage() (which only bounds file-offset-relative pointers). Every such pointer is now validated against the ELF's own live PT_LOAD footprint before it is dereferenced.
• Adds overflow-safe helpers resolveSymbol() and resolveImportAddr() used by both relocation loops, and hardens getSymbolCount()'s DT_GNU_HASH bucket/bloom/chain walk against attacker-controlled sizes and offsets (all arithmetic validated in a wide integer type before forming any pointer).
• Clamps DT_STRSZ to the room actually left in strtab's own live segment, fixing string-table lookups that were previously either unbounded (trusting a corrupted DT_STRSZ) or over-strict (rejecting small, otherwise-valid libraries).
• Caps the DT_GNU_HASH chain-terminator scan (MAX_GNU_HASH_CHAIN_SCAN, 1M entries) so a corrupted table that never sets its terminator bit can't turn into a very long scan of a large live segment while Symbols::_parse_lock is held.

Motivation:
Production crash since tracer v1.56.1:

ElfParser::parseDynamicSection()+0x158
ElfParser::parseProgramHeaders(CodeCache*, char const*, char const*, bool)+0xf8
Symbols::parseLibraries(CodeCacheArray*, bool)+0x4c0
Libraries::updateSymbols(bool)+0xc
Profiler::start(Arguments&, bool)+0x84c

The DT_HASH case in parseDynamicSection() dereferenced a dyn_ptr()-derived pointer with no bounds check — a single malformed DT_HASH entry crashed the process. This was the one path in symbols_linux.cpp not routed through any bounds check (everything else already used inImage() for file-offset-relative data). Rather than special-casing just DT_HASH, this fixes the underlying gap: every virtual-address-relative pointer computed via at()/dyn_ptr() in this file is now validated the same way, so the same class of bug can't resurface at DT_GNU_HASH, the relocation tables, or the SFrame/eh_frame_hdr sections.

Additional Notes:

• MAX_PLAUSIBLE_SEGMENT_SIZE (4 GiB) caps how large a single PT_LOAD segment is trusted to be, guarding the pointer arithmetic in plausibleSegmentEnd()/liveSegmentEnd()/liveImageEnd() against wraparound from a corrupted p_memsz.
• Ran this PR's own diff through a review pass; found and fixed two issues before merging:
  • The DT_GNU_HASH chain scan had no iteration cap, so a corrupted table landing in a large (now up to 4 GiB) live segment with its terminator bit never set could scan for a very long time, one inLiveImage() (O(e_phnum)) call at a time, while holding Symbols::_parse_lock. Added MAX_GNU_HASH_CHAIN_SCAN to bound this to a fast failure instead.
  • Removed a dead strtab_room == 0 branch in parseDynamicSection(): dyn_ptr() already guarantees strtab lies strictly inside a live segment before returning non-NULL, so that branch could never be taken.
  • at()/dyn_ptr() computed _vaddr_diff + p_vaddr (or + d_ptr) unconditionally; an untrusted p_vaddr/d_ptr large enough overflows that pointer addition (undefined behavior, and on wraparound could alias back into a plausible-looking live address). Both now validate the addition in integer space first and reject the entry (at() returns false, dyn_ptr() returns nullptr) instead of forming an overflowing pointer; all 5 call sites were updated to check the result.

How to test the change?:
ddprof-lib/src/test/cpp/elfparser_ut.cpp adds extensive coverage, including:

• dynamicSectionHashPointerOutOfBounds: a regression test reproducing the exact production crash via a crafted DT_HASH pointer (must not crash, must not populate symbols).
• Per-guard coverage isolating resolveSymbol()/resolveImportAddr() against a malformed syment, symbol index, or r_offset in .rela.plt entries.
• atProgramHeaderVaddrOverflow / dynPtrOverflow: regression tests for the at()/dyn_ptr() overflow guard, using p_vaddr/d_ptr == UINT64_MAX to force the pointer addition to overflow.

Run on Linux: ./gradlew :ddprof-lib:gtestDebug_elfparser_ut (or gtestRelease_elfparser_ut).

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 security review (run the dd:platform-security-review
  skill, or file a request via the PSEC review form).
  bewaire also runs automatically on every PR.
• This PR doesn't touch any of that.
• JIRA: PROF-15982

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