Android: Add field_enter_after_edit[] formspec element

[grorp]

The problem

The other day, there was a discussion on Discord about automatically submitting formspecs when closing the Android text input dialog. Here is a small excerpt:

rollerozxa: someone raised an issue to me about rollertest that some settings wouldn't save in the new dialog. in reality it's caused by the fact you can't easily set settings with an input dialog without pressing the set button on android

rollerozxa: on desktop you're able to simply press enter and it will be set, so it would be neat if there could be a little hack that automatically presses enter on input boxes once submitted from the native dialog (either just in the settings dialog or everywhere)

grorp: Doing this (automatically pressing enter when closing the input dialog) everywhere would cause problems in the "Join Game" tab. You'd enter your username, exit the input dialog, and then Minetest would automatically try to join the server. You wouldn't even have a chance to enter a password.

rollerozxa: yeah it would need to be enabled per formspec I think

The discussion starts at https://discord.com/channels/369122544273588224/369137254641303560/1152532281408372788.

The solution

This PR introduces a new formspec element:

### `field_enter_after_edit[<name>;<enter_after_edit>]`

* Only affects Android clients.
* `<name>` is the name of the field.
* If `<enter_after_edit>` is true, pressing the "Done" button in the Android
  text input dialog will simulate an <kbd>Enter</kbd> keypress.
* Defaults to false when not specified (i.e. no tag for a field).

This also works for textareas, btw. There are already many use cases for this in builtin alone. I've enabled enter_after_edit for the following fields:

• Serverlist search
• ContentDB search
• New settings dialog search
• New settings dialog settings
• Devtest "chest of everything" / "bag of everything" search

I'm open to suggestions for better solutions to this problem.

To do

This PR is a Ready for Review.

How to test

Verify that pressing the "Done" button in the Android text input dialog still doesn't trigger an Enter keypress by default. Verify that it does trigger an Enter keypress in the cases mentioned above.

CC @rollerozxa

[rollerozxa]

Haven't tested it but looks good and should fix the issue I was describing, thanks!

[srifqi]

I tested this PR. It looks good to me.

[grorp]

Thank you for reviewing!

A question for the formspec gurus: Do I have to bump the formspec version in this PR? I don't think so since I haven't changed any existing elements, I've only added a new one, but I'm not sure.

[grorp]

I've increased the formspec version now.
https://irc.minetest.net/minetest-dev/2023-09-28#i_6118407

[grorp]

Marked the element as experimental according to a discussion on IRC.
https://irc.minetest.net/minetest-dev/2023-09-30#i_6118679

[Montandalar]

I'm glad you were able to have a fruitful discussion on Discord, but viewing that conversation requires an account, and even with being logged in, I get a "no text channels" error message. I assume I need to join the server, but the server information wasn't given.

In contrast, IRC discussions all get logged and are easily viewable on irc.minetest.net. Thankfully, you included the relevant parts of discussion here. I just hope that if you're going to continue using Discord for these kinds of conversations, you always include all the important info on GitHub. But #minetest-dev would be good to use in my opinion.

Edit: Okay, to my surprise, the Discord is listed on minetest.net. Whatever I think of that, it's still really annoying to need an account with a 3rd party to view conversations.