Fix handling of exotic identifiers for let bindings in GenType #9777

Job	Run time
test-devcontainer	17m 53s
build-compiler (ubuntu-24.04-arm, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, t...	7m 46s
build-compiler (ubuntu-24.04, ocaml-variants.5.0.0+options,ocaml-option-static, linux-x64, x86_64...	7m 16s
build-compiler (windows-2025, 5.3.0, true, win32-x64, x86_64-pc-windows-gnu, .exe)	14m 46s
build-compiler (macos-15, 5.3.0, true, darwin-arm64, aarch64-apple-darwin)	8m 39s
build-compiler (macos-15-intel, 5.3.0, true, darwin-x64, x86_64-apple-darwin)	17m 1s
build-compiler (ubuntu-24.04, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, linux...	7m 35s
pkg-pr-new	52s
api-docs	1m 49s
test-integration-rewatch (macos-15)	4m 52s
test-integration-rewatch (ubuntu-24.04)	3m 33s
test-installation-pnpm (macos-15)	17s
test-integration-rewatch (macos-15-intel)	6m 12s
test-installation-npm (macos-15-intel)	27s
test-installation-npm (ubuntu-24.04)	14s
test-installation-npm (ubuntu-24.04-arm)	20s
test-installation-npm (macos-15)	21s
test-integration-rewatch (windows-2025)	7m 8s
test-installation-pnpm (ubuntu-24.04)	13s
test-installation-pnpm (ubuntu-24.04-arm)	15s
test-installation-pnpm (macos-15-intel)	38s
test-installation-npm (windows-2025)	2m 59s
test-installation-pnpm (windows-2025)	36s
test-integration-rewatch (ubuntu-24.04-arm)	2m 48s
publish	-1s
	1h 54m 29s

Provide feedback