Merge branch '2023-10-12-expo-add-support-for-edting-lines-of-text'

To quote the author:
So far expo only supports menus. These are quite flexible for various
kinds of settings, but cannot deal with free-form input, such as a
serial number or a machine name.

This series adds support for a textline object, which is a single line
of text. It has a maximum length and its value is stored within the expo
structure.

U-Boot already has a command-line editor which provides most of the
features needed by expo. But the code runs in its own loop and only
returns when the line is finished. This is not suitable for expo, which
must handle a keypress at a time, returning to its caller after each
one.

In order to use the CLI code, some significant refactoring is included
here. This mostly involves moving the internal loop of the CLI to a
separate function and recording its state in a struct, just as was done
for single keypresses some time back. A minor addition is support for
Ctrl-W to delete a word, since strangely this is currently only present
in the simple version.

The video-console system provides most of the features needed by
testline, but a few things are missing. This series provides:

- primitive cursor support so the user can see where he is typing
- saving and restoring of the text-entry context, so that expo can allow
  the user to continue where he left off, including deleting previously
  entered characters correctly (for Truetype)
- obtaining the nominal width of a string of n characters, so that a
  suitable width can be chosen for the textline object

Note that no support is provided for clearing the cursor. This was
addressed in a previous series[1] which could perhaps be rebased. For
this implementation, the cursor is therefore not enabled for the normal
command line, only for expo.

Reading and writing textline objects is supported for FDT and
environment, but not for CMOS RAM, since it would likely use too much
RAM to store a string.

In terms of code size, the overall size increase is 180 bytes for
Thumb02 boards, 160 of whcih is the addition of Ctrl-W to delete a word.

[1] https://patchwork.ozlabs.org/project/uboot/list/?series=280178&state=*

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