Export: Unify settings for PC texture formats, removed obsoleted ETC feature

[akien-mga]

S3TC and BPTC should always be used together, and likewise for ETC2 and ASTC.

Also removes obsolete ETC support code since we removed that format.

• Supersedes Validate texture format selection when exporting to Windows or Linux #84913, implementing Validate texture format selection when exporting to Windows or Linux #84913 (comment).
• Fixes Resource is not exported correctly to PCK file #81234.
• Fixes Exported game crashes due to missing resources while in-editor it runs fine #86317.
• Closes Add warning about export missing BPTC texture format (or change export settings) godot-proposals#7230.

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I didn't add compatibility code yet, it would be a bit convoluted in EditorExportPreset::_set which currently has its own logic for some visibility update. Could be done but I'm not sure it's worth the bother, when handling this minor compat breakage just requires ensuring that the proper formats are toggled in the settings. The default behavior for the new options is also to export S3TC/BPTC, which is the most likely combinations that users need.

Haven't tested much yet.

For a potential 4.2.x cherry-pick we might consider going with the approach in #84913 to be more conservative.

[akien-mga]

Removed this, which is redundant with the above logic, and also wrong if users for some reason decide to export ETC2/ASTC and not S3TC/BPTC.

[akien-mga]

I kept KTX_TTF_ETC1_RGB here as we seem to handle only RGB here.
The options are:

        // ETC1-2
        KTX_TTF_ETC1_RGB = 0,
            /*!< Opaque only. Returns RGB or alpha data, if
                 KTX_TF_TRANSCODE_ALPHA_DATA_TO_OPAQUE_FORMATS flag is
                 specified. */
        KTX_TTF_ETC2_RGBA = 1,
            /*!< Opaque+alpha. EAC_A8 block followed by an ETC1 block. The
                 alpha channel will be opaque for textures without an alpha
                 channel. */

        // Values for automatic selection of RGB or RGBA depending if alpha
        // present.
        KTX_TTF_ETC = 22,
            /*!< Automatically selects @c KTX_TTF_ETC1_RGB or
                 @c KTX_TTF_ETC2_RGBA according to presence of alpha. */

[BlueCube3310]

The color data encoding is ETC1 for all of them anyway, so there should not be any quality difference.

[fire]

I took an initial look at this, but we probably need to try the pr on all the devices on platforms we support like:

• Web (Windows, Mac, iOS, Android)
• Windows (amd64)
• Linux (amd64)
• Mac (Apple Silicon)
• ios (arm64)
• android (arm64)

[clayjohn]

Looks great to me!