Port getSyntacticNullishnessSemantics changes

[Andarist]

ports microsoft/TypeScript#60440
ports microsoft/TypeScript#60616
ports microsoft/TypeScript#60402

[Copilot]

Pull Request Overview

Ports updates from TypeScript PRs to align nullish-coalescing predicate semantics in the Go checker and its test baselines.

• Removes obsolete nullishness errors from the predicateSemantics baselines.
• Adds TaggedTemplateExpression and MetaProperty to always-truthy cases.
• Introduces handling for the comma operator by recursing into its right operand.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
testdata/baselines/reference/.../predicateSemantics.errors.txt.diff	Removed extra ?? unreachable-operand error entries.
testdata/baselines/reference/.../predicateSemantics.errors.txt	Updated expected error count and pruned removed entries.
internal/checker/checker.go	Added TaggedTemplateExpression, MetaProperty, and a comma-operator case.

Comments suppressed due to low confidence (1)

internal/checker/checker.go:12287

• Matching on ast.KindCommaToken will never occur because node.Kind represents expression node kinds (e.g., ast.KindBinaryExpression), not operator tokens. Move comma handling into the ast.KindBinaryExpression case by checking node.AsBinaryExpression().OperatorToken.Kind == ast.KindCommaToken.

case ast.KindCommaToken: