[JSC] Refine SyntaxError message for generator method parsing failure

[shvaikalesh]

17d1d74

[JSC] Refine SyntaxError message for generator method parsing failure
https://bugs.webkit.org/show_bug.cgi?id=264368
<rdar://problem/118081884>

Reviewed by Justin Michaud.

This change rewords SyntaxError message, thrown in case of generator method parsing failure,
to mention "method" rather than "function", aligning error wording for sync generator functions
with async counterparts.

Also, tweaks the helper to return "generator function" instead of "generator" for GeneratorBodyMode,
which is unobservable yet matches the terminology of the spec [1].

[1]: https://tc39.es/ecma262/#sec-generator-objects

* JSTests/stress/generator-class-methods-syntax.js:
* JSTests/stress/regress-189292.js:
* Source/JavaScriptCore/parser/Parser.cpp:
(JSC::stringForFunctionMode):

Canonical link: https://commits.webkit.org/270379@main

c8b0137

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim		✅ 🧪 jsc-armv7-tests
	✅ 🛠 watch		⏳ 🛠 jsc-mips
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim		⏳ 🧪 jsc-mips-tests

[webkit-early-warning-system]

EWS run on previous version of this PR (hash e692dd3)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	⏳ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	🧪 gtk-wk2
❌ 🛠 🧪 jsc	🧪 api-ios	✅ 🧪 mac-wk2	🧪 api-gtk
❌ 🛠 🧪 jsc-arm64	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim		❌ 🧪 jsc-armv7-tests
	✅ 🛠 watch		⏳ 🛠 jsc-mips
	✅ 🛠 watch-sim		⏳ 🧪 jsc-mips-tests

[justinmichaud]

rs=me

[webkit-early-warning-system]

Starting EWS tests for c8b0137. Live statuses available at the PR page, #20131

[webkit-early-warning-system]

EWS run on current version of this PR (hash c8b0137)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim		✅ 🧪 jsc-armv7-tests
	✅ 🛠 watch		⏳ 🛠 jsc-mips
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim		⏳ 🧪 jsc-mips-tests

[webkit-commit-queue]

Committed 270379@main (17d1d74): https://commits.webkit.org/270379@main

Reviewed commits have been landed. Closing PR #20131 and removing active labels.