Fix grid-area resolution edge cases in resolve_absolute_grid_area

[nicoburns]

Objective

Fix edge cases in DetailedGridTracksInfo::resolve_absolute_grid_area where the resolved area diverged from browser behaviour (verified against Chrome via new generated fixtures):

• Out-of-grid check ran before normalization. Placements are now resolved to a pair of sorted lines first, and only then are lines falling outside the grid treated as auto. Pseudo-diff:

    placement
      .resolve_line_names(...)
      .into_origin_zero(...)
  -   .map(|p| if line out of [min_line, max_line] { Auto } else { p })
      .resolve_absolutely_positioned_grid_tracks()
  +   .map(|line| line.filter(|l| min_line <= l && l <= max_line))

  This makes e.g. grid-column: 3 / 1 (swapped lines) and a non-existent named line like foo / 3 (which resolves past the explicit grid end) match Chrome: on a 2-column grid, foo / 3 resolves to the area between line 3 and the end padding edge.
• Empty axes. An axis with no tracks still contains one grid line, positioned by content alignment. DetailedGridTracksInfo gains a pub empty_axis_line: Option<f32> field recording that line's position, used as a fallback before the padding-edge fallback.

Context

Extracted from the OOF-hoisting stack (#1147, originally in #1145) since it applies to main independently — resolve_absolute_grid_area already exists here. The stack will be restacked without this commit once it lands.

Also adds named-line support (grid-template-columns/rows line names and named placements) to the gentest fixture format, plus 5 Chrome-generated fixtures covering out-of-range lines, unknown/known named lines, padding-edge lines, and empty grids.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/65c5463061c8403bade7888271d5eeb4
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/65c5463061c8403bade7888271d5eeb4?variant=devin-insiders
Requested by: @nicoburns

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