Bug 35455: Remove = in ICU for indexing/searching

Bug 35455: Remove = in ICU for indexing/searching

This change more closely aligns ICU and CHR so that ICU also
removes the = character. This fixes issues in ICU when searching
with a : which gets transformed into a =. Without this change,
the Analytics features won't work for titles with a colon in them.

Test plan:
0. Apply the patch and import bibs from Bugzilla (using Staged MARC tools)
1. cp ./etc/zebradb/etc/phrases-icu.xml /etc/koha/zebradb/etc/phrases-icu.xml
2. cp ./etc/zebradb/etc/words-icu.xml /etc/koha/zebradb/etc/words-icu.xml
3. vi /etc/koha/zebradb/etc/default.idx
Change "charmap word-phrase-utf.chr" to "icuchain words-icu.xml" for "index w"
and "icuchain phrases-icu.xml" for "index p"
4. koha-zebra --stop kohadev
5. pkill zebrasrv
6. koha-zebra --start kohadev
7. koha-rebuild-zebra -a -b -f -v kohadev

8. Search for "Awesome title" and open the detail page
9. Note that the "Analytics: Show analytics" line shows up
10. Click that link
11. Note that it opens the "Cool article" record and it displays
"In: Awesome title: awesome subtitle"
12. Click that link
13. Note that it opens the "Awesome title" record

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 7375d82c408ad6963cf3f3cae060b9376ffca91a)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>