Add mbstring functions#1

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andarut wants to merge 15 commits intomasterfrom

Commits on Apr 7, 2023

fix issue
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Commits on Apr 10, 2023

mbstring functions
andarut
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Commits on Apr 17, 2023

Commits on Apr 19, 2023

finish basic mbstring functions and building libmbfl
andarut
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Commits on Apr 30, 2023

add MBFL flag to runtime, restore mbstring functions for only UTF-8 and Windows-1251 encodings and add runtime declarations of all mbstring functions
andarut
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small fixes
andarut
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