fix(compiler): convert absolute length units to pixels

[YevheniiKotyrlo]

Problem

in, cm, mm, Q, pt and pc are absolute lengths: css-values-4 §6.2 fixes each against the inch, 1in = 96px, so each has an exact pixel value. parseLength warns and drops all six, so on native a declaration holding one sets nothing - width: 1in, border-top-width: 3pt, margin: 1in 1pc - and neither does a variable that resolves at runtime or a media query such as (min-width: 4in).

Solution

parseLength converts the six units to pixels through one table, ABSOLUTE_UNIT_PIXELS in src/utilities/absolute-units.ts. Every route reads a length through parseLength, so declarations, shorthands, transforms, shadows, font sizes, variables and media queries all convert, with or without inlineRem; lightningcss already folds a calc() mixing them with px.

Tests

src/__tests__/native/absolute-units.test.tsx renders each unit as a declaration and through a variable declared twice, with inlineRem: false, in a media query and in a shorthand. All 15 fail on main. The expected values are css-values-4's ratios, rounded as the compiler rounds every length.

Verification

On Ubuntu with the workflow's steps - build, lint, typecheck, yarn test, node --test node/__tests__/*.mjs, both library builds, the web export, the unstaged-changes checks and commitlint - everything passes.

Not run: the iOS and Android example builds.

Unchanged: an absolute length set from JavaScript through vars() reaches React Native as the string it was given.

Device evidence, before and after: #492 (comment)

Merge order

It shares lines with #389 (compiler/declarations.ts, utilities/index.ts), #391 (compiler/declarations.ts, utilities/index.ts), #413 (compiler/declarations.ts), #417 (compiler/declarations.ts), #420 (compiler/declarations.ts, utilities/index.ts), #491 (compiler/declarations.ts, utilities/index.ts), #494 (compiler/declarations.ts, utilities/index.ts), #495 (compiler/declarations.ts, utilities/index.ts); whichever lands second rebases.

[YevheniiKotyrlo]

Device evidence — before / after

UNFIXED — Only the control is 96 pixels wide. Every other bar spans the row, because a width in an absolute unit other than px is dropped.

FIXED — Every bar is as wide as the control: an inch is 96 pixels, and centimetres, millimetres, quarter-millimetres, points and picas convert through it.

before — 3.1.0-rc.0	after — with this PR

Android 16 emulator (API 36, GLES on the host GPU), 1140×2400 @ 480dpi, both frames from one run. before is the published 3.1.0-rc.0 plus what my test app needs from my other patches to run: the native and native-internal subpath exports, PR 459, cascade-layer ranking, and a shim that compiles a class-qualified :root inert. after adds the rest of my open PRs, this one included. One of them shows on every screen: PR 417 narrows a var()-valued font-family to one family, so the after sets its text in the theme's face where the before falls back to the platform's.