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.
We have a `g_debug_ToConsole` variable. However, so far this was
always set to true and output to `syslog`. This change modifies
the default to `false`, and in that case logs to `syslog`. If
`g_debug_ToConsole` is true we no output to the console.
When running the KMX unit tests we set `g_debug_ToConsole` to true.
Turns out that @darcywong00's suggestion for a test case was a Very Good
Idea. The SMP handling in Keyman Core had an egregious bug where only
half of a surrogate pair was being deleted in the UTF-16 context; see
kmx_processor.cpp 425-428. This was then masked by the test runner
masking the damage in the original test case; see kmx.cpp 193-203.
The new test case exercises a number of additional ways of manipulating
the context where surrogate pairs exist, to show we handle the deletion
properly within Keyman Core and in the test runner.
