[WGSL] Clean up AST nodes created during compilation

[tadeuzagallo]

8f03835

[WGSL] Clean up AST nodes created during compilation
https://bugs.webkit.org/show_bug.cgi?id=257328
rdar://109833858

Reviewed by Mike Wyrzykowski.

We allocate new nodes during compilation, and since we can compile the
same module multiple times, that could lead to unbounded memory growth.
In order to fix that, we save the state of the allocator before we start
a new compilation and erase all objects allocate after that point once
we are done compiling. That is safe since we already revert all AST
modifications in a similar manner.

* Source/WebGPU/WGSL/AST/ASTBuilder.cpp:
(WGSL::AST::Builder::saveCurrentState):
(WGSL::AST::Builder::restore):
* Source/WebGPU/WGSL/AST/ASTBuilder.h:
* Source/WebGPU/WGSL/WGSL.cpp:
(WGSL::prepareImpl):
* Source/WebGPU/WGSL/WGSLShaderModule.h:
(WGSL::ShaderModule::Compilation::Compilation):
(WGSL::ShaderModule::Compilation::~Compilation):

Canonical link: https://commits.webkit.org/264571@main

edc32f8

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		✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
❌ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash edc32f8)

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		✅ 🧪 gtk-wk2
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🧪 api-gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2
	✅ 🛠 tv-sim
❌ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 264571@main (8f03835): https://commits.webkit.org/264571@main

Reviewed commits have been landed. Closing PR #14349 and removing active labels.