maint(common): consolidate functions to determine OS

[ermshiperete]

We have at least three different functions to determine the current OS. From #14049 (comment):

We have a similar test in build-utils.sh and in builder.inc.sh... It would be good to have this in just one place. I am okay with this being a separate refactor task because there is a bit of a tangle with /resources/builder.inc.sh, /resources/build/builder.inc.sh, /resources/build/build-utils.sh, and /resources/shellHelperFunctions.sh that we need to sort out also.

keyman/resources/builder.inc.sh

Lines 2068 to 2080 in 7d33ff7

	fi
	# --- Detect tools ---
	local builder_installed_tools=()
	# Detect delphi compiler (see also delphi_environment.inc.sh)
	if [[ $builder_platform == win ]]; then
	local ProgramFilesx86="$(cygpath -w -F 42)"
	if [[ -x "$(cygpath -u "$ProgramFilesx86\\Embarcadero\\Studio\\20.0\\bin\\dcc32.exe")" ]]; then
	builder_installed_tools+=(delphi)
	fi
	fi

keyman/resources/build/build-utils.sh

Lines 208 to 224 in 4645d14

	_builder_get_operating_system() {
	declare -g BUILDER_OS
	# Default value, since it's the most general case/configuration to detect.
	BUILDER_OS=linux
	# Subject to change with future improvements.
	if [[ $OSTYPE == darwin* ]]; then
	BUILDER_OS=mac
	elif [[ $OSTYPE == msys ]]; then
	BUILDER_OS=win
	elif [[ $OSTYPE == cygwin ]]; then
	BUILDER_OS=win
	fi
	readonly BUILDER_OS
	}
	_builder_get_operating_system

and #14049 introduced:

keyman/resources/teamcity/includes/tc-helpers.inc.sh

Lines 3 to 30 in 9939ef9

	# Returns 0 if we're running on Ubuntu.
	is_ubuntu() {
	if [[ "${OSTYPE:-}" == "linux-gnu" ]]; then
	return 0
	else
	return 1
	fi
	}
	# Returns 0 if we're running on Windows, i.e. if the environment variable
	# `OSTYPE` is set to "msys" or "cygwin".
	is_windows() {
	if [[ "${OSTYPE:-}" == "msys" ]] || [[ "${OSTYPE:-}" == "cygwin" ]]; then
	return 0
	else
	return 1
	fi
	}
	# Returns 0 if we're running on macOS.
	is_macos() {
	if [[ "${OSTYPE:-}" == "darwin" ]]; then
	return 0
	else
	return 1
	fi
	}

See also:

• maint(common): consolidate builder and related scripts #14065
• chore: rename one of the builder.inc.sh includes #13789
• feat(common): establish builder.typescript.inc.sh and friends #12744