Shift+Home/End selects to end of line

[jamesreprise]

What is the goal of this PR?

Matching the way navigating with the Home & End keys works, adding the shift key should only select to the end of the line rather than the end of the file.

What are the changes implemented in this PR?

SELECT_HOME and SELECT_END only select to the start of the line and the end of the line rather than the start of the file and the end of the file respectively.

Also refactored the names of functions that move the cursor to the start or end of the file to make that fact explicit rather than implicit.

Additional info

Closes https://github.com/vaticle/typedb-studio/issues/555

[typedb-bot]

PR Review Checklist

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Code

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