Thai vowels are excluded in search index

What are the steps required to reproduce the bug?

Assuming hook_preprocess() separates Thai words by space, just let search module index any nodes with Thai words, e.g., "ผู้ ใหญ่ บ้าน".

What behavior were you expecting?

Thai words should be indexed correctly including their vowels, e.g., "ผู้ ใหญ่ บ้าน".

What happened instead?

All Thai vowels are replaced by space because they are categorized as "Mn" in UnicodeData.txt, e.g., "ผ ใหญ บาน". In particular, below vowels should be not treated "Mn" and "Po" in Thai language like Latin-based languages.

0E31;THAI CHARACTER MAI HAN-AKAT;Mn;0;NSM;;;;;N;THAI VOWEL SIGN MAI HAN-AKAT;;;;
0E34;THAI CHARACTER SARA I;Mn;0;NSM;;;;;N;THAI VOWEL SIGN SARA I;;;;
0E35;THAI CHARACTER SARA II;Mn;0;NSM;;;;;N;THAI VOWEL SIGN SARA II;;;;
0E36;THAI CHARACTER SARA UE;Mn;0;NSM;;;;;N;THAI VOWEL SIGN SARA UE;;;;
0E37;THAI CHARACTER SARA UEE;Mn;0;NSM;;;;;N;THAI VOWEL SIGN SARA UEE;sara uue;;;
0E38;THAI CHARACTER SARA U;Mn;103;NSM;;;;;N;THAI VOWEL SIGN SARA U;;;;
0E39;THAI CHARACTER SARA UU;Mn;103;NSM;;;;;N;THAI VOWEL SIGN SARA UU;;;;
0E3A;THAI CHARACTER PHINTHU;Mn;9;NSM;;;;;N;THAI VOWEL SIGN PHINTHU;;;;
0E47;THAI CHARACTER MAITAIKHU;Mn;0;NSM;;;;;N;THAI VOWEL SIGN MAI TAI KHU;mai taikhu;;;
0E48;THAI CHARACTER MAI EK;Mn;107;NSM;;;;;N;THAI TONE MAI EK;;;;
0E49;THAI CHARACTER MAI THO;Mn;107;NSM;;;;;N;THAI TONE MAI THO;;;;
0E4A;THAI CHARACTER MAI TRI;Mn;107;NSM;;;;;N;THAI TONE MAI TRI;;;;
0E4B;THAI CHARACTER MAI CHATTAWA;Mn;107;NSM;;;;;N;THAI TONE MAI CHATTAWA;;;;
0E4C;THAI CHARACTER THANTHAKHAT;Mn;0;NSM;;;;;N;THAI THANTHAKHAT;;;;
0E4D;THAI CHARACTER NIKHAHIT;Mn;0;NSM;;;;;N;THAI NIKKHAHIT;nikkhahit;;;
0E4E;THAI CHARACTER YAMAKKAN;Mn;0;NSM;;;;;N;THAI YAMAKKAN;;;;
0E4F;THAI CHARACTER FONGMAN;Po;0;L;;;;;N;THAI FONGMAN;;;;

Currently, PREG_CLASS_SEARCH_EXCLUDE includes below vowels.

\x{e31}\x{e34}-\x{e3f}\x{e46}-\x{e4f}\x{e5a}\x{e5b}

It should be replaced by below.

\x{e3f}\x{e46}\x{e5a}\x{e5b}

Note that I mark it critical because we can't use search module with Thai content at all.