world: Add LV symbols

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This adds symbols used in Latvian language, as options in world.yaml. The newly added character definitions are commented out and requires the user to enable them if needed. This is done due to size issues - read below in Drawbacks.

Compositions

Composition definitions have been added for the new symbols. Since these don't affect the keymap.dtsi on their own, they are added without commenting them out.

Consonants

Since 9c943ca the consonants have been grouped together in a single character group. I don't think it's as useful when the number of different consonants is larger than the few in this group, thus I have added groups for the individual base characters.

I would prefer if the individual consonant letters would have their own letter grouping, same as vowels.

Drawbacks

On v42-rc8, if all added character definitions are uncommented, the resulting keymap.dtsi will be too large to successfully build in the layout editor, presenting a vague error such as "Error time: Sat, 27 Dec 2025 19:00:46 GMT". This is one of the reasons

In order to build, it is necessary to either:

1. remove some unnecessary character definitions from world.yaml. This will reduce the amount of macros in keymap.dtsi, and thus the size of the file.
2. remove some of the unnecessary keyboard layers before attempting to rebuild in layout editor.

Usage

To use the new symbols, user would have to:

1. Uncomment the necessary definitions in characters: object;
2. Add additional transforms if necessary;
3. remove any unnecessary definitions in characters:, enuring there are no references to removed characters in transforms. The duplicates in consonants are probably a good start, but will likely not be enough.
4. rebuild with rake or ./rake;
5. paste the contents of keymap.dtsi into the layout editor;
6. update the key bindings in the layout editor as needed;
7. (optional) remove unnecessary layers;
8. build;

Either (2) or (6) needs to be done to avoid build error, although I have not tested on the newest DEV releases, which already removed some layers - maybe the reduction would already be sufficient.