feat: add es2026 as a valid target and lib

[Oleksandr Tarasiuk (a-tarasyuk)]

Fixes #63704

[Copilot]

Pull request overview

Adds ES2026 compiler-target and standard-library support, including the APIs requested by #63704.

Changes:

• Registers es2026 as a target, default standard target, and library.
• Adds ES2026 API declarations and preserves esnext.* aliases.
• Adds conformance tests and refreshes generated baselines.

Reviewed changes

Copilot reviewed 136 out of 540 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/typescript/src/enums/scriptTarget*.ts	Exposes ES2026 publicly.
packages/typescript/test/{async,sync}/api.test.ts	Updates target diagnostics.
tsc/internal/core/{compileroptions,scripttarget_stringer_generated}.go	Defines and formats the target.
tsc/internal/tsoptions/enummaps.go	Registers target, libraries, and compatibility aliases.
tsc/internal/transformers/estransforms/definitions.go	Selects the ES2026 transform pipeline.
tsc/internal/checker/utilities.go	Adds ES2026 library suggestions.
tsc/internal/bundled/libs/lib.es2026*.d.ts	Defines the ES2026 library and APIs.
tsc/internal/bundled/libs/lib.esnext.d.ts	Makes ESNext inherit ES2026.
tsc/internal/bundled/{embed_generated,libs_generated}.go	Embeds and registers new libraries.
tsc/internal/compiler/program_test.go	Updates expected ESNext library ordering.
tsc/testdata/fixtures/compiler/*.ts	Synchronizes compiler fixtures.
tsc/testdata/tests/cases/conformance/es2026/*.ts	Tests ES2026 APIs and diagnostics.
tsc/testdata/baselines/reference/**	Refreshes generated compiler, build, watch, API, and conformance baselines.

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