[Webkit-unassigned] [Bug 257200] New: Ignore bidi control characters while collecting fallback fonts

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257200

            Bug ID: 257200
           Summary: Ignore bidi control characters while collecting
                    fallback fonts
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: afalke at igalia.com
                CC: mmaxfield at apple.com

https://drafts.csswg.org/css-text-3/#white-space-processing
"Unsupported Default_ignorable characters must be ignored for text rendering."

As mentioned in 245154 at main, taking zero width glyphs (e.g. control characters) into consideration while collecting fallback font information
may result in incorrect line height and baseline positioning; an alternative mentioned in 245154 at main was to check against unicode ranges to omit
certain glyphs.

246121 at main fixed a regression in which bidi control chars rendered, and replaced our previous hardcoded list of Default_ignorable characters with the helper
function,FontCascade::isCharacterWhoseGlyphsShouldBeDeletedForTextRendering (also refactored in 260081 at main). That helper function covers the use case 'rightToLeftOverride' which the test `LayoutTests/fast/text/fallback-font-and-zero-width-glyph.html`, currently marked as failing in glib, relies on.

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