Merge bitcoin/bitcoin#22151: build: Follow Transifex docs to prepare XLIFF source

985d85e Follow Transifex docs to prepare XLIFF source (Hennadii Stepanov)

Pull request description:

  This PR is a #21694 follow up.

  From the Transifex [docs](https://docs.transifex.com/formats/xliff#how-to-distinguish-between-a-source-file-and-a-translation-file):
  > A source file is different than a translation file. The translation file contains \<Target> references, whereas a source file does not.

  This PR makes the `qt/locale/bitcoin_en.xlf` source file according to the docs.

ACKs for top commit:
  laanwj:
    ACK 985d85e

Tree-SHA512: 537ef78f39a12f094b17fc902c5b59c7ae4d27e5fa35fbf6b33386843e4521236dac3275ba26ff2d1c435e53e8942284644d5de67b0b3543cec96cbcd4351607

Author: laanwj

src/Makefile.qt.include

@@ -359,11 +359,15 @@ $(srcdir)/qt/bitcoinstrings.cpp: FORCE
 	@test -n $(XGETTEXT) || echo "xgettext is required for updating translations"
 	$(AM_V_GEN) cd $(srcdir); XGETTEXT=$(XGETTEXT) COPYRIGHT_HOLDERS="$(COPYRIGHT_HOLDERS)" $(PYTHON) ../share/qt/extract_strings_qt.py $(libbitcoin_node_a_SOURCES) $(libbitcoin_wallet_a_SOURCES) $(libbitcoin_common_a_SOURCES) $(libbitcoin_zmq_a_SOURCES) $(libbitcoin_consensus_a_SOURCES) $(libbitcoin_util_a_SOURCES)
 
+# The resulted bitcoin_en.xlf source file should follow Transifex requirements.
+# See: https://docs.transifex.com/formats/xliff#how-to-distinguish-between-a-source-file-and-a-translation-file
 translate: $(srcdir)/qt/bitcoinstrings.cpp $(QT_FORMS_UI) $(QT_FORMS_UI) $(BITCOIN_QT_BASE_CPP) qt/bitcoin.cpp $(BITCOIN_QT_WINDOWS_CPP) $(BITCOIN_QT_WALLET_CPP) $(BITCOIN_QT_H) $(BITCOIN_MM)
 	@test -n $(LUPDATE) || echo "lupdate is required for updating translations"
 	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(LUPDATE) -no-obsolete -I $(srcdir) -locations relative $^ -ts $(srcdir)/qt/locale/bitcoin_en.ts
 	@test -n $(LCONVERT) || echo "lconvert is required for updating translations"
-	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(LCONVERT) -o $(srcdir)/qt/locale/bitcoin_en.xlf -i $(srcdir)/qt/locale/bitcoin_en.ts
+	$(AM_V_GEN) QT_SELECT=$(QT_SELECT) $(LCONVERT) -drop-translations -o $(srcdir)/qt/locale/bitcoin_en.xlf -i $(srcdir)/qt/locale/bitcoin_en.ts
+	@$(SED) -i.old -e 's|source-language="en" target-language="en"|source-language="en"|' -e '/<target xml:space="preserve"><\/target>/d' $(srcdir)/qt/locale/bitcoin_en.xlf
+	@rm -f $(srcdir)/qt/locale/bitcoin_en.xlf.old
 
 $(QT_QRC_LOCALE_CPP): $(QT_QRC_LOCALE) $(QT_QM)
 	@test -f $(RCC)