[refactor] Make linkifyStackTraceTopFrame() easier to reason about.
[refactor] Make linkifyStackTraceTopFrame() easier to reason about.

This CL doesn't change behavior, but instead deals with making the
`Linkifier.linkifyStackTraceTopFrame()` method easier to reason about
and easier, in particular regarding when the `fallbackAnchor` is
actually used.

Drive-by-cleanup: Make `Linkifier.createLink()` return both the link and
the linkInfo, since all call sites use both and previously had dead code
that would check for absence of linkInfo.

Bug: chromium:1272413, chromium:1270248, chromium:1271078
Change-Id: Iecb4371ef3d5261d46b05fc2005f16a0da5ef176
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3295523
Auto-Submit: Benedikt Meurer <024a1e0af501338d11c3b837c6193d11c140d792@chromium.org>
Commit-Queue: Kim-Anh Tran <a72f38a79b5fac6811022b8a7fb84830d856c9c9@chromium.org>
Reviewed-by: Kim-Anh Tran <a72f38a79b5fac6811022b8a7fb84830d856c9c9@chromium.org>

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