Fix code generation for emojis in polyvars and labels #8288

Job	Run time
build-compiler (ubuntu-24.04, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, linux...	2m 36s
build-compiler (windows-2022, 5.3.0, true, win32-x64, x86_64-pc-windows-gnu)	4m 9s
build-compiler (macos-13, 5.3.0, true, darwin-x64, x86_64-apple-darwin)	6m 27s
build-compiler (macos-14, 5.3.0, true, darwin-arm64, aarch64-apple-darwin)	2m 59s
build-compiler (ubuntu-24.04, ocaml-variants.4.14.2+options,ocaml-option-static, linux-x64, x86_6...	17m 0s
build-compiler (ubuntu-24.04-arm, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, t...	4m 14s
api-docs	11s
pkg-pr-new	56s
test-integration-rewatch (ubuntu-24.04-arm)	57s
test-integration-rewatch (macos-14)	1m 10s
test-integration-rewatch (ubuntu-24.04)	49s
test-integration-rewatch (macos-13)	1m 33s
test-integration-rewatch (windows-2022)	1m 35s
test-installation-npm (macos-14)	16s
test-installation-pnpm (macos-13)	31s
test-installation-pnpm (ubuntu-24.04)	12s
test-installation-npm (windows-2022)	32s
test-installation-pnpm (macos-14)	21s
test-installation-npm (ubuntu-24.04)	14s
test-installation-pnpm (ubuntu-24.04-arm)	17s
test-installation-npm (macos-13)	34s
test-installation-pnpm (windows-2022)	35s
test-installation-npm (ubuntu-24.04-arm)	19s
publish	0s
	48m 27s

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