fix(mapping): Report a single frame when no line number and no signature are present

[markushi]

Tombstone stacktraces have no line numbers and no signatures — a frame is
just a.b.c. When every mapping entry for the method is keyed by a
minified line range, nothing can select one, and we emitted every entry
whenever their original names differed. Since R8 reuses one obfuscated name
for many unrelated bodies, a single frame can quickly expand into hundreds
of unrelated frames.

This PR mimics retracer's behavior by reporting only the first range group's
outermost entry. Inlinees are dropped, because we don't have enough information.

Verified frame-for-frame against retrace 8.9.27 on inline chains (2- and
3-deep), a chain followed by distinct ranges, real overloads, and against the original issue report.

Also changes behavior beyond the reported bug: test_inline_group_no_base_entries
and its cache twin asserted a 3-frame expansion for a line-less frame and now
assert the single outermost frame, confirmed against retrace.

Fixes JAVA-646

[linear-code]

JAVA-646

[cursor]

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