Improved TextEdit::add_selection_for_next_occurrence test case
Improved TextEdit::add_selection_for_next_occurrence test case

It covers additional selections of different words, as well manually adding a cursor in between and selecting the next occurrence. The previous test also was outdated in regards of not testing the implicit call to `select_word_under_caret` made by `add_selection_for_next_occurrence` in case there's no selection.

sanikoyes/godot,godotengine/godot,sanikoyes/godot,sanikoyes/godot,BastiaanOlij/godot,pkowal1982/godot,BastiaanOlij/godot,pkowal1982/godot,pkowal1982/godot,sanikoyes/godot,godotengine/godot,godotengine/godot,sanikoyes/godot,godotengine/godot,sanikoyes/godot,godotengine/godot,godotengine/godot,pkowal1982/godot,BastiaanOlij/godot,BastiaanOlij/godot,godotengine/godot,BastiaanOlij/godot,pkowal1982/godot,pkowal1982/godot,sanikoyes/godot,pkowal1982/godot,BastiaanOlij/godot,godotengine/godot,BastiaanOlij/godot,BastiaanOlij/godot,sanikoyes/godot,pkowal1982/godot