lib: add Math.sumPrecise type definition (ES2026 / esnext)

[VanshBD]

Fixes #63427

Summary

Adds type definition for Math.sumPrecise, which reached TC39 Stage 4
on 2025-07-28 and is part of ES2026.

Changes

• src/lib/esnext.math.d.ts — new file with Math.sumPrecise definition
• src/lib/esnext.d.ts — added esnext.math reference
• src/lib/libs.json — registered esnext.math lib target
• src/compiler/commandLineParser.ts — added lib.esnext.math.d.ts target

Placement rationale

Math.sumPrecise reached Stage 4 on 2025-07-28, after the ES2025 cutoff.
Correctly placed under esnext following the same pattern as other
esnext domain libs (esnext.array, esnext.date, etc.)

References

• TC39 Proposal: https://github.com/tc39/proposal-math-sum
• Stage 4 notes: https://github.com/tc39/notes/blob/main/meetings/2025-07/july-28.md
• MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sumPrecise

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a new esnext.math lib to expose Math.sumPrecise in the TypeScript standard library surface area.

Changes:

• Register new esnext.math lib in the lib registry (libs.json) and CLI lib name mapping (commandLineParser.ts)
• Add esnext.math to the esnext umbrella lib references (esnext.d.ts)
• Introduce src/lib/esnext.math.d.ts defining Math.sumPrecise(numbers: Iterable<number>)

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/lib/libs.json	Adds esnext.math to the known lib list
src/lib/esnext.math.d.ts	Declares the new Math.sumPrecise API
src/lib/esnext.d.ts	References esnext.math from the esnext umbrella lib
src/compiler/commandLineParser.ts	Enables --lib esnext.math name-to-file resolution

[VanshBD]

@microsoft-github-policy-service agree