Convert to curly quotes & Check curly quotes (#517)

* Add Convert to curly quotes feature

This commit makes the changes.
Second commit will check for suspects.

* Add Check curly Quotes feature

Pops a dialog listing suspected quote errors such as
quote at start/end of line or after/before space when
curl is the wrong direction, or open quote preceded
by word character, or paragraph end without closing
double quotes (unless next para begins with double
quotes), unconverted straight quotes.

Dialog has several buttons that make corrections,
and also supports Cmd/Ctrl+left/right click to make
best guess fix, which is to convert to open curly if
quote is straight, or to swap open & close if quote
is curly.

After Convert to Curly Quotes is run, the Check is run
automatically.  However, unlike GG1, the conversion to
curly quotes does notneed to be done with the convert
feature for the check to work. So if the user makes
manual quote changes at any point they can just
re-run the check.

* Review fixes

1. Add `T'ain't` to custom contractions list
2. Change label for Swap Quote/Space button

src/guiguts/application.py

@@ -59,6 +59,8 @@
     DEFAULT_SCANNOS_DIR,
     DEFAULT_REGEX_SCANNOS,
     DEFAULT_STEALTH_SCANNOS,
+    convert_to_curly_quotes,
+    check_curly_quotes,
 )
 from guiguts.page_details import PageDetailsDialog
 from guiguts.preferences import preferences, PrefKey
@@ -700,6 +702,8 @@ def init_tools_menu(self) -> None:
         menu_tools.add_button("R~ewrap Selection", self.file.rewrap_selection)
         menu_tools.add_button("C~lean Up Rewrap Markers", self.file.rewrap_cleanup)
         menu_tools.add_separator()
+        menu_tools.add_button("Convert to Curly ~Quotes", convert_to_curly_quotes)
+        menu_tools.add_button("Check Curly Q~uotes", check_curly_quotes)
         unmatched_menu = Menu(menu_tools, "Un~matched")
         unmatched_menu.add_button("Bloc~k Markup...", unmatched_block_markup)
         unmatched_menu.add_button("~DP Markup...", unmatched_dp_markup)

src/guiguts/maintext.py

@@ -1343,7 +1343,7 @@ def _replace_preserving_pagemarks(
             )
 
     def _replace_preserving_pagemarks_block(
-        self, start_index: Any, end_index: Any, replacement: str, *tags: Any
+        self, start_point: Any, end_point: Any, replacement: str, *tags: Any
     ) -> None:
         """Replace text indicated by indexes with given string (& optional tags).
 
@@ -1362,6 +1362,9 @@ def _replace_preserving_pagemarks_block(
             replacement:  Replacement text.
             tags: Optional tuple of tags to be applied to inserted text.
         """
+        # Convert input args to index because if marks, can get odd behavior depending on gravity.
+        start_index = self.index(start_point)
+        end_index = self.index(end_point)
         # Get lengths from start of replacement to each page marker
         len_to_marks: list[int] = []
         mark = end_index