switch the Western language list box to SvxLanguageComboBox

This allows the user to assign an arbitrary (but valid) BCP 47 language
tag to a portion of text, so that customized spell-checkers or other
language-dependent tools can be used without the need to wait for
LibreOffice to add yet another language to the list in the next release.

+bool SvtLanguageTable::HasLanguageType()

(cherry picked from commit 2a8eff589a53c8dd65e18d7a9d11cdb98a937e68)

+ SvxLanguageComboBox EditModifyHdl(), SaveEditedAsEntry()

(cherry picked from commit 29c024afbe6a46459e37c5ceec510de1cd0ca7c8)

handle SvxLanguageComboBox edit

(cherry picked from commit 1aad7628dcd7fd14d48814d00c3d04e4ec0c59d5)

finally switch the Western language list box to SvxLanguageComboBox

(cherry picked from commit dbe8b3b6d4f2d2cc2e8c702b78034e9013f71e8f)

advance start of edit selection on a matching entry

... to allow continuous typing.

(cherry picked from commit fe2b8ef18b11b226fddd1cf3fc7f9133426a1b1a)

Change-Id: Id57eb51b69e50be78f85d19a7b3623c1acdf6509
Reviewed-on: https://gerrit.libreoffice.org/9447
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>