Optimize for size in preamble.js/postamble.js. NFC

[sbc100]

• Regarding using throw e vs reject(e), these are defined to be the same thing inside the new Promise executor function.

The following (34) test expectation files were updated by running the tests with --rebaseline:

codesize/test_codesize_cxx_ctors1.json: 151862 => 151770 [-92 bytes / -0.06%]
codesize/test_codesize_cxx_ctors2.json: 151265 => 151173 [-92 bytes / -0.06%]
codesize/test_codesize_cxx_except.json: 195756 => 195666 [-90 bytes / -0.05%]
codesize/test_codesize_cxx_except_wasm.json: 166986 => 166894 [-92 bytes / -0.06%]
codesize/test_codesize_cxx_except_wasm_legacy.json: 164870 => 164778 [-92 bytes / -0.06%]
codesize/test_codesize_cxx_lto.json: 120704 => 120613 [-91 bytes / -0.08%]
codesize/test_codesize_cxx_mangle.json: 262235 => 262145 [-90 bytes / -0.03%]
codesize/test_codesize_cxx_noexcept.json: 153862 => 153770 [-92 bytes / -0.06%]
codesize/test_codesize_cxx_wasmfs.json: 179611 => 179516 [-95 bytes / -0.05%]
test/codesize/test_codesize_file_preload.expected.js updated
codesize/test_codesize_file_preload.json: 23778 => 23755 [-23 bytes / -0.10%]
codesize/test_codesize_files_js_fs.json: 18225 => 18134 [-91 bytes / -0.50%]
codesize/test_codesize_files_wasmfs.json: 63692 => 63596 [-96 bytes / -0.15%]
codesize/test_codesize_hello_O0.json: 38459 => 38329 [-130 bytes / -0.34%]
codesize/test_codesize_hello_O1.json: 8708 => 8596 [-112 bytes / -1.29%]
codesize/test_codesize_hello_O2.json: 6132 => 6042 [-90 bytes / -1.47%]
codesize/test_codesize_hello_O3.json: 5827 => 5737 [-90 bytes / -1.54%]
codesize/test_codesize_hello_Os.json: 5815 => 5725 [-90 bytes / -1.55%]
codesize/test_codesize_hello_Oz.json: 4988 => 4893 [-95 bytes / -1.90%]
codesize/test_codesize_hello_dylink.json: 44130 => 44025 [-105 bytes / -0.24%]
codesize/test_codesize_hello_dylink_all.json: 855887 => 855789 [-98 bytes / -0.01%]
codesize/test_codesize_hello_export_nothing.json: 3119 => 3026 [-93 bytes / -2.98%]
codesize/test_codesize_hello_single_file.json: 5139 => 5042 [-97 bytes / -1.89%]
codesize/test_codesize_hello_wasmfs.json: 5827 => 5737 [-90 bytes / -1.54%]
codesize/test_codesize_libcxxabi_message_O3.json: 3516 => 3422 [-94 bytes / -2.67%]
codesize/test_codesize_libcxxabi_message_O3_standalone.json: 3696 => 3603 [-93 bytes / -2.52%]
codesize/test_codesize_mem_O3.json: 9516 => 9422 [-94 bytes / -0.99%]
codesize/test_codesize_mem_O3_grow.json: 9802 => 9708 [-94 bytes / -0.96%]
codesize/test_codesize_mem_O3_grow_standalone.json: 9653 => 9556 [-97 bytes / -1.00%]
codesize/test_codesize_mem_O3_standalone.json: 9510 => 9417 [-93 bytes / -0.98%]
codesize/test_codesize_mem_O3_standalone_lib.json: 8707 => 8612 [-95 bytes / -1.09%]
codesize/test_codesize_mem_O3_standalone_narg.json: 8828 => 8735 [-93 bytes / -1.05%]
codesize/test_codesize_mem_O3_standalone_narg_flto.json: 7759 => 7666 [-93 bytes / -1.20%]
codesize/test_unoptimized_code_size.json: 176271 => 176073 [-198 bytes / -0.11%]

Average change: -0.87% (-2.98% - -0.01%)