fix(linux): Fix switching to keyboard in middle of line (#4678)

Don't re-set context if it changed because the cursor location was
wrong. When the user switches to the EuroLatin keyboard in the
middle of the line, we're getting a wrong cursor location. This will
be fixed with the next keypress, but it leads to the context string
suddenly having more characters added to the front. If we re-set the
context because it's different now we will loose the information we
previously added to the context.

We now compare the end of the string. If the new context string ends
with the old context string we assume that the cursor position got
updated and don't re-set the context.

This fixes #4678.