Select frame when fetching a frame variable in DAP

Select frame when fetching a frame variable in DAP

Right now, if a program uses multiple languages, DAP value formatting
will always use the language of the innermost frame.  However, it is
better to use the variable's defining frame instead.  This patch does
this by selecting the frame first.

This also fixes a possibly latent bug in the "stepOut" command --
"finish" is sensitive to the selected frame, but the DAP code may
already select other frames when convenient.  The DAP stepOut request
only works on the newest frame, so be sure to select it before
invoking "finish".