fdo#76294: Properly intern string literals in formula on xls import.

(cherry picked from commit b09426b83c12b0cd27cd909602251cb076ffa4ba)
(cherry picked from commit 625c595fc30d2e6153735dc2ed2359ff4f8a1e3a)
(cherry picked from commit 6bb7fa8df523d3ae7b9945009fb1034f28cb0a0a)

Conflicts:
	formula/source/core/api/token.cxx
	include/formula/tokenarray.hxx
	sc/source/filter/excel/excform.cxx
	sc/source/filter/excel/excform8.cxx
	sc/source/filter/excel/frmbase.cxx
	sc/source/filter/inc/XclImpChangeTrack.hxx
	sc/source/filter/inc/lotform.hxx
	sc/source/filter/inc/qproform.hxx
	sc/source/filter/lotus/lotform.cxx
	sc/source/filter/lotus/lotimpop.cxx
	sc/source/filter/lotus/op.cxx
	reportdesign/source/ui/inc/Formula.hxx

Change-Id: Icf962a4363887f323da6d2bdf935a027df3319fa
Reviewed-on: https://gerrit.libreoffice.org/9008
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>