[JSC] Disallow yield/await expressions in class field initializers

[dhecht]

36f50aa

[JSC] Disallow yield/await expressions in class field initializers
https://bugs.webkit.org/show_bug.cgi?id=276438
rdar://119044881

Reviewed by Yusuke Suzuki.

The language spec doesn't explictly disallow yield and await expressions
in class field initializers, however it implicitly does given that
the expression is effectively evaluated as if it's inside a method.
Additionally, the consensus seems to be that these expressions
should not be allowed, see:

tc39/ecma262#3333

The yield and await expressions are now handled differently, but
similar to how they are each handled in other contexts. This also
seems to be the least disruptive way to handle existing scripts,
as well as consistent with other engines:

yield: raise syntax error
await: parse as an identifier

Also adding a new test that generates and verifies scripts containing
a class with a field initializer containing yield and await, where the
class is either not nested or nested inside generator or async functions
to verify the behavior of various combinations.

* Source/JavaScriptCore/parser/Parser.cpp:
(JSC::Parser<LexerType>::parseYieldExpression):
(JSC::Parser<LexerType>::parseAwaitExpression):
(JSC::Parser<LexerType>::parsePrimaryExpression):
(JSC::Parser<LexerType>::parseUnaryExpression):

Canonical link: https://commits.webkit.org/280837@main

4748971

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

[webkit-early-warning-system]

EWS run on current version of this PR (hash 4748971)

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

[Constellation]

r=me

[webkit-commit-queue]

Committed 280837@main (36f50aa): https://commits.webkit.org/280837@main

Reviewed commits have been landed. Closing PR #30660 and removing active labels.