fix: match a dataSet value and a dir attribute the way the DOM does

[YevheniiKotyrlo]

Problem

On main:

1. A false dataSet value is absent to [data-x]. react-native-web writes a dataSet entry as a data-* attribute for every value except null and undefined (createDOMProps), so [data-test] matches dataSet={{ test: false }} on the web. The runtime treats false as absent there, as it rightly does for a boolean prop such as disabled.
2. An array dataSet value compares as no value. The DOM holds the array's comma-joined text, so [data-test="a,b"] matches dataSet={{ test: ["a", "b"] }}.
3. [dir="RTL"] never matches. HTML compares a dir value ASCII case-insensitively, so the selector matches dir="rtl" unless it carries the s flag. The compiler emits the operand as written, and the direction condition compares it literally.

Solution

• dataSet values. A dataSet value is present unless it is nullish, and it compares as the text the DOM holds. A plain prop keeps its boolean-attribute rule, so false is still absent there.
• dir operands. The compiler folds a dir operand to lowercase unless the selector carries s.
• Shared ASCII folding. Both folds use one ASCII lowercasing helper, which the runtime's i flag also uses. toLowerCase would also fold U+212A KELVIN SIGN onto k.

Tests

Every case renders as Chromium 153, Firefox 155 and WebKit 26.6 do.

• src/__tests__/native/attributes.test.tsx:
  • [data-test] over false, 0, "", null and undefined;
  • [disabled] over a false prop;
  • = and ~= over an array value.
• src/__tests__/compiler/selectors.test.tsx covers the condition [dir=…] compiles to, in each case and with the i and s flags.
• src/__tests__/native/direction-media.test.tsx renders [dir="RTL"], [dir="RTL" i] and [dir="RTL" s] against a right-to-left layout.
• On main, 7 of the 45 cases in these files fail. Each of 7 mutations fails its own cases.

Verification

On Windows with Node 26:

• yarn lint clean
• yarn typecheck clean
• yarn test --coverage: every failure also fails on main on this machine (the four babel cases)
• yarn build clean
• yarn example expo export --platform web exported

Merge order

• fix(compiler): read [class=…] from the prop the class list arrives on #448 and fix(compiler): drop a namespace-qualified attribute selector #449 change the same attribute-selector build sites, and build on this PR. This one lands first, and each of them carries its commit until it does.
• fix(native): answer :dir() per element, and compile every spelling of it #459 changes how dir reads the direction. Whichever lands second keeps this PR's folded operand.

Base

Re-written on main (a5002c5). #451 already answers the rest of Selectors §6 the way this PR did on its old base: exact comparison, whitespace and dash-match boundaries, the empty-operand exclusions and the i flag. Its tests cover those, so this PR no longer carries them.

[YevheniiKotyrlo]

No current device pair

Every build of my test app carries this change: the app's reading-direction code needs #459, which is built on #447, #448 and #449. So no build can show the before, and the description's tests are the evidence.