Warnings im code caused by the recent refactoring in the expression parser

Requirements

• I searched through the issues if the issue already exists

Steps to reproduce

1. Compile
2. Start the application

Expected

No extensive warnings during the compile step or on app start.

Observed

the new c-array _functions[] is using i18n() and is initialized before main() is evaluated where KLocalizedString::setApplicationDomain("labplot2") is called. This leads to the numerous warning like

kf.i18n: KLocalizedString: Using an empty domain, fix the code. msgid: "Linear" msgid_plural: "" msgctxt: ""

(one warning for every string in _functions[]). We need to set the domain prior to using i18n().

Also, there are multiple compiler warnings for functions.cpp:

Labplot Version

Debug build 2.10.0-1082-gc131be535
Oct 23 2023, 09:12:52
System: openSUSE Leap 15.4
Locale: English,United States (Decimal point '.', Group separator ','
Number settings: Decimal point '.', Group separator ',', Exponential 'e', Zero digit '0', Percent '%', Positive/Negative sign '+'/'-' (Updated on restart)
Architecture: x86_64-little_endian-lp64
Kernel: linux 5.14.21-150400.24.81-default
C++ Compiler: GNU 12.3.0
C++ Compiler Flags: -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -Wall -Wextra -Wundef -Wpointer-arith -Wunreachable-code -Wunused -Wdeprecated-declarations -fno-omit-frame-pointer -fstack-protector -fexceptions -std=c++17 -O2 -Wcast-align -Wswitch-enum -fvisibility=default -pedantic -Wzero-as-null-pointer-constant