Rename hasToString() to findUsesToString()

There are special cases where the toString() exist,
but still plaintext() is not to be used by find.

(cherry picked from commit 8de81e8dc1)

src/Paragraph.cpp

@@ -4425,7 +4425,7 @@ docstring Paragraph::asString(pos_type beg, pos_type end, int options, const Out
 		else if (c == META_INSET && (options & AS_STR_INSETS)) {
 			if (c == META_INSET && (options & AS_STR_PLAINTEXT)) {
 				LASSERT(runparams != nullptr, return docstring());
-				if (runparams->find_effective() && getInset(i)->hasToString())
+				if (runparams->find_effective() && getInset(i)->findUsesToString())
 					getInset(i)->toString(os);
 				else
 					getInset(i)->plaintext(os, *runparams);

src/insets/Inset.h

@@ -350,7 +350,7 @@ public:
 	virtual docstring xhtml(XMLStream &, OutputParams const &) const;
 
 	/// 
-	virtual bool hasToString() const { return false; }
+	virtual bool findUsesToString() const { return false; }
 	/// Writes a string representation of the inset to the odocstream.
 	/// This one should be called when you want the whole contents of
 	/// the inset.

src/insets/InsetBranch.h

@@ -80,7 +80,7 @@ private:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetCitation.h

@@ -62,7 +62,7 @@ public:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetCounter.h

@@ -43,7 +43,7 @@ public:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetHyperlink.h

@@ -34,7 +34,7 @@ public:
 	///
 	bool isInToc() const override { return true; }
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetIPAMacro.h

@@ -154,7 +154,7 @@ public:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetQuotes.h

@@ -157,7 +157,7 @@ public:
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetRef.h

@@ -65,7 +65,7 @@ public:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetSpace.h

@@ -136,7 +136,7 @@ public:
 	///
 	void validate(LaTeXFeatures & features) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetSpecialChar.h

@@ -82,7 +82,7 @@ public:
 	///
 	docstring xhtml(XMLStream &, OutputParams const &) const override;
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///

src/insets/InsetText.h

@@ -180,7 +180,7 @@ public:
 	///
 	void setMacrocontextPositionRecursive(DocIterator const & pos);
 	///
-	bool hasToString() const override { return true; }
+	bool findUsesToString() const override { return true; }
 	///
 	void toString(odocstream &) const override;
 	///