cairo: enable font backends and fractional glyph positioning in 1.18.4.bcr.1 (#10389) PangoCairo cannot link against the existing Cairo BCR module because its build omits the FreeType/fontconfig backend. The existing configuration also selects a rendering path that rounds fractional glyph positions to whole pixels. This PR fixes both issues while keeping the same upstream Cairo 1.18.4 source release. BCR's [add-only policy](https://github.com/bazelbuild/bazel-central-registry/blob/main/docs/README.md#add-only) requires build fixes to be published as a new revision. The existing `modules/cairo/1.18.4/` build files are therefore copied into `modules/cairo/1.18.4.bcr.1/` and modified there. This explains why GitHub shows mostly added files: much of the diff is the existing overlay copied into the new version directory. The revision makes four changes: 1. **Enable the font backend Pango needs.** In `overlay/src/BUILD.bazel`, compile the existing upstream sources `cairo-ft-font.c`, `cairo-colr-glyph-render.c`, and `cairo-svg-glyph-render.c`. Add the existing BCR FreeType and fontconfig dependencies, enable `CAIRO_HAS_FT_FONT` and `CAIRO_HAS_FC_FONT`, and declare the supported FreeType feature macros. This exposes the font APIs required by PangoCairo. Cairo continues to depend on the original FreeType 2.14.1 module, independently of the separate PNG-support revision. 2. **Preserve fractional glyph positions.** Set `HAS_PIXMAN_GLYPHS=1`, matching upstream Cairo's configuration for the required Pixman version. Without this setting, Cairo selects a legacy compositor that rounds glyph positions to integers; a glyph intended at 10.25 pixels is snapped to a whole-pixel position. The change enables upstream's existing Pixman glyph cache. 3. **Add two portable regression tests.** `ft_smoke` renders an embedded bitmap glyph through both the FreeType-face and fontconfig-pattern APIs. `glyph_positioning` compares a synthetic square glyph with equivalent vector geometry at all 16 quarter-pixel phase combinations; it fails when the glyph cache is disabled. Both tests run without installed fonts, alongside the existing Cairo test. 4. **Correct existing build and test configuration.** Declare `HAVE_ZLIB` for the already-present zlib dependency so the script interpreter compiles; correct `PACKAGE_VERSION` from 1.18.5 to the actual 1.18.4 release; and fix the existing Bazel test-path patch's pointer handling so it compiles with GCC 14. Validation: all Cairo targets and three tests pass independently on Ubuntu x86_64 with Bazel 7.7.1, 8.4.2, and 9.2.0, using the original FreeType module. The integrated tests also pass on Debian 13/GCC 14 with all three Bazel versions, and with optimized Clang 18 on Bazel 9.2.0. The existing CI matrix is retained. Local BCR content validation passed using checksum-verified cached release archives after download-host timeouts; the remaining platforms and original download URLs were not verified locally.
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