evas_textblock: markup: handle invalid/missing escape characters

Summary:
T8088

if escape character sequence not found for example **&123;** :
* (Old Behaviour)  : Draw nothing
* (New Behaviour)  : Draw Text like it plain text

I think this is the right behaviour since:
1- We print output as it is, so user can detect what was the problem.
   For example user write &gf; (by mistake, he wanted to write >)
   == if we nothing is printed he would not know exactly where is the real problem.
      it can be font file, textblock is not visible, he may think bug in efl
   == if we printed &gf; as it is, it will direclty show that this is not valid escape char.
2- If user made mistake in text, it is better to show it instead of hide it, maybe there are new sequences that we do not know about.

This behaviour was checked on multible systems:
1- Web Browsers like chrome
2- Qt
3- Android

They all have same as our new behaviour

Example :
markup text =  ">&gf;
Old              :     >
New            :     >&gf;

Test Plan:
```
#define EFL_EO_API_SUPPORT 1
#define EFL_BETA_API_SUPPORT 1

#include <Eina.h>
#include <Elementary.h>
#include <Efl_Ui.h>

static void
_gui_quit_cb(void *data EINA_UNUSED, const Efl_Event *event EINA_UNUSED)
{
   efl_exit(0);
}

static void
_gui_setup()
{
   Eo *win, *box;

   win = efl_add(EFL_UI_WIN_CLASS, efl_main_loop_get(),
                 efl_ui_win_type_set(efl_added, EFL_UI_WIN_TYPE_BASIC),
                 efl_text_set(efl_added, "Hello World"),
                 efl_ui_win_autodel_set(efl_added, EINA_TRUE));

   // when the user clicks "close" on a window there is a request to delete
   efl_event_callback_add(win, EFL_UI_WIN_EVENT_DELETE_REQUEST, _gui_quit_cb, NULL);

   box = efl_add(EFL_UI_BOX_CLASS, win,
                efl_content_set(win, efl_added),
                efl_gfx_hint_size_min_set(efl_added, EINA_SIZE2D(360, 240)));

   efl_add(EFL_UI_TEXT_CLASS, box,
           efl_text_markup_set(efl_added,
           "&gt;&gf;"),
           efl_text_interactive_selection_allowed_set(efl_added, EINA_FALSE),
           efl_gfx_hint_weight_set(efl_added, 1.0, 0.9),
           efl_gfx_hint_align_set(efl_added, 0.5, 0.5),
           efl_text_multiline_set(efl_added,EINA_FALSE),
           efl_pack(box, efl_added));

   efl_add(EFL_UI_BUTTON_CLASS, box,
           efl_text_set(efl_added, "Quit"),
           efl_gfx_hint_weight_set(efl_added, 1.0, 0.1),
           efl_pack(box, efl_added),
           efl_event_callback_add(efl_added, EFL_UI_EVENT_CLICKED,
                                  _gui_quit_cb, efl_added));
}

EAPI_MAIN void
efl_main(void *data EINA_UNUSED, const Efl_Event *ev EINA_UNUSED)
{
   _gui_setup();
}
EFL_MAIN()
```

Reviewers: woohyun, bowonryu, segfaultxavi, bu5hm4n

Reviewed By: segfaultxavi

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9428

src/lib/evas/canvas/evas_object_textblock.c

@@ -7931,6 +7931,8 @@ _prepend_escaped_char(Efl_Text_Cursor_Cursor *cur_obj, const char *s,
    escape = _escaped_char_get(s, s_end);
    if (escape)
      evas_textblock_cursor_text_prepend(cur_obj, escape);
+   else /* Use same text input if no escape was found */
+     _prepend_text_run(cur_obj, s, s_end);
 }