Start-time optimizations

[garazdawi]

This PR optimizes the startup time of init, kernel and escripts by keeping a minimal list of modules that are used during boot and loading those in parallel before they are used. Doing this reduces startup time by 7-25% depending on scenario.

Probe	Master (ms)	Tip (ms)	Faster
erl -noshell -eval 'erlang:halt().'	72.5	66.9	−7.8%
escript (source/compile)	119.2	89.5	−24.9%
escript (interpret)	90.8	74.2	−18.2%
escript (precompiled)	72.3	65.0	−10.2%

The escripts just call erlang:halt/0 directly in main/1.

Measured on my M5 Mac.

While experimenting I tried two other things that did not give any measurable improvements:

1. Don't load unicode_util when using latin-1 string functions.
   unicode_util:gc and dc are used by string functions even if the string does not contains any unicode characters, so I tried inlining those functions into the string module to make sure that the huge unicode_util modules is not loaded when not needed. Turns out that is takes very little time to load a single module and that there was no measurable gain.
2. Async loading of inet_db. When starting inet_db it reads quite a few files and takes a few ms to do, but doing that start async turned out to be quite hard and error prone and in the end it did not save all that much anyway.

The PR also includes two smaller drive-by fixes.

[github-actions]

CT Test Results

     7 files     615 suites   3h 22m 21s ⏱️
 6 283 tests  5 765 ✅ 516 💤 2 ❌
12 512 runs  11 908 ✅ 602 💤 2 ❌

For more details on these failures, see this check.

Results for commit b124845.

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// Erlang/OTP Github Action Bot

[bjorng]

Each start script has a list of modules that will be loaded in parallel by init (the first primLoad tuple in the start script). The list of those modules are found here:

otp/lib/sasl/src/systools_make.erl

Lines 1541 to 1577 in 51a9da0

	mandatory_modules() ->
	[error_handler, %Truly mandatory.
	%% Modules that are almost always needed. Listing them here
	%% helps the init module to load them faster. Modules not
	%% listed here will be loaded by the error_handler module.
	%%
	%% Keep this list sorted.
	application,
	application_controller,
	application_master,
	code,
	code_server,
	erl_eval,
	erl_lint,
	erl_parse,
	error_logger,
	ets,
	file,
	filename,
	file_server,
	file_io_server,
	gen,
	gen_event,
	gen_server,
	heart,
	kernel,
	logger,
	logger_filters,
	logger_server,
	logger_backend,
	logger_config,
	logger_simple_h,
	lists,
	proc_lib,
	supervisor
	].

That list of modules were last updated in 2018.

Perhaps you could update that list to be the minimum set of modules that will always/almost always be needed and add a test case to ensure that it remains up-to-date.

[garazdawi]

Perhaps you could update that list to be the minimum set of modules that will always/almost always be needed and add a test case to ensure that it remains up-to-date.

Yes, that is part of this PR already.