Improve TextEdit and CodeEdit documentation

[kitbdev]

• fixes Auto Brace Complete editor setting is incorrectly described #98260
• The descriptions for get_visible_line_count and get_total_visible_line_count in particular seemed to be swapped.
• Removes Sets whether and Sets if.
• Uses [member ProjectSettings.input/...] for actions (and found ui_text_unindent is actually supposed to be ui_text_dedent).
• Adds references to related methods, members, and theme items.
• Adds details in some places that were lacking.

[Loff3]

I've suggested a few small changes to the wording that might help improve clarity.

[Loff3]

Suggested change

	Unindents all lines that are selected or have a caret on them. Uses spaces or a tab depending on [member indent_use_spaces]. Same as performing the [member ProjectSettings.input/ui_text_dedent] action. See [method indent_lines].
	Unindents all selected lines or lines containing a caret. Uses spaces or a tab depending on [member indent_use_spaces]. Equivalent to performing the [member ProjectSettings.input/ui_text_dedent] action. See [method indent_lines].

[kitbdev]

For lines that are selected or have a caret on them I made it this way to match other descriptions for consistency.
Also in your suggestion, it should be and instead of or to avoid ambiguity.

[kitbdev]

Added auto brace completion description in Editor Settings as well.

• for Auto Brace Complete editor setting is incorrectly described #98260

[Mickeon]

Thank you very, very much for changing these for the better. These descriptions were written really awkwardly, but there could be work to do still.

[Mickeon]

You used "overwritable" elsewhere too, plus that's part of name of the actual method.

Suggested change

	If [code]true[/code], the gutter lines can be overridden when using [method merge_gutters]. See [method is_gutter_overwritable].
	If [code]true[/code], the gutter lines can be overwritable when using [method merge_gutters]. See [method is_gutter_overwritable].

Also worth keeping in mind that this makes the subject way more ambiguous. "the gutter lines" could be referring to all of the gutters, but this method requires a gutter index to be passed.

[kitbdev]

"overwritable" means "can be overridden", so I'm not sure this suggestion is right. Also I am trying to describe the scenario when it may be overridden. When true it is always "overwritable".

I'll change "the gutter lines" to "lines of the gutter at the given index".

Edit: actually it's more accurate to say "line data of the gutter at the given index can be overridden..."
Its stuff like the icon, color, and metadata that are stored per line that get overridden.

[kitbdev]

Rebased and applied suggestions.
I think I got everywhere that I already touched for the gutter at index or given line. I changed a few others, but there is more that I didn't change.
Also added descriptions for a few more methods like CodeEdit::can_fold_line and TextEdit::get_indent_level.

[Mickeon]

Get ready for a huge second pass revision by yours truly just to ensure we don't have to do this again for a loooong while.

I am really happy about this and I must congratulate you for the hard work.

[Mickeon]

No beating around the bush. All of this is a huge improvement.

[Repiteo]

Thanks!