DEPS: Bump @swc/core from 1.15.18 to 1.15.21

[dependabot]

Bumps @swc/core from 1.15.18 to 1.15.21.

• Release notes
• Changelog
• Commits

[github-actions]

PR body updated to plaintext for easier squash-merging. Original body content below:

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Bumps @swc/core from 1.15.18 to 1.15.21.

Changelog

Sourced from @​swc/core's changelog.

[1.15.21] - 2026-03-22

Bug Fixes

• (cli) Honor externalHelpers=false in rust binary (#11693) (1be052e)

• (cli) Skip mkdir when --out-file targets the current directory (#11720) (f3f4e51)

• (es/decorators) Resolve 2022-03 issues #9565/#9078/#9079 and add regressions (#11698) (a025d2b)

• (es/fixer) Wrap new opt chain (#11618) (fdcd184)

• (es/flow) Normalize module await bindings for Hermes parity (#11703) (73d8761)

• (es/minifier) Fix compatibility for Wasm plugin (swc_ast_unknown) (#11641) (abd0e45)

• (es/module) Preserve explicit index.js import path when baseUrl is set (#11597) (830dbeb)

• (es/module) Avoid rewriting unknown relative extensions (#11713) (ed09218)

• (es/regexp) Implement transform-named-capturing-groups-regex (#11642) (f62bfa9)

• (es/types) Add new options types (#11683) (62eeee1)

• (malloc) Fallback to system allocator on linux gnu s390x/powerpc (#11606) (e103fac)

• Update lz4_flex to resolve RUSTSEC-2026-0041 (#11701) (7528507)

Documentation

• (agents) Improve guidance (#11626) (1cdfec9)

• (agents) Add AGENTS two-pass rules for es crates (#11634) (12af4a1)

... (truncated)

Commits

• a06c4b9 chore: Publish 1.15.21 with swc_core v59.0.1
• eb169d5 chore: Publish 1.15.21-nightly-20260322.3 with swc_core v59.0.1
• 4c378f7 chore: Publish 1.15.21-nightly-20260322.2 with swc_core v59.0.1
• 1cdd010 chore: Publish 1.15.21-nightly-20260322.1 with swc_core v59.0.1
• de0c918 chore: Publish 1.15.20-nightly-20260302.1 with swc_core v58.0.4
• f79f31e chore: Publish 1.15.19-nightly-20260302.1 with swc_core v58.0.3
• 357255d feat(bindings): Add linux ppc64le and s390x support across npm bindings (#11602)
• See full diff in compare view

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