scripts: kconfig: Add incremental search to menuconfig
scripts: kconfig: Add incremental search to menuconfig

Pressing [/] brings up a dialog with an edit box where a regex can be
entered. The list of matching symbols is always shown below it.
Selecting a symbol and pressing [Enter] jumps directly to it in the menu
tree. If the symbol is invisible, show-all mode is turned on
automatically.

This commit also includes a bunch of more-or-less unrelated changes from
poking around with the code:

  - Some redundant styles were merged. Probably wouldn't want to have a
    different style for each separator line, for example...

  - [ESC] in the top menu now works like [Q]

  - Returning to a parent menu now makes sure that the selected row is
    visible, even if the terminal was shrunk between entering the child
    menu and leaving it.

  - A _max_scroll() helper was factored out to reduce code duplication.
    It takes a list of items and a window in which the list is
    displayed, with one row per item, and returns the minimum scroll
    value that will make the final item visible.

  - The save dialog now pops up a message to confirm that the save was
    successful.

  - Lots of minor code nits all over (renamings, etc.)

Signed-off-by: Ulf Magnusson <f650684f780c6b48c0158c4e0f2e27f74aabc755@gmail.com>

zephyrproject-rtos/zephyr,kraj/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,zephyriot/zephyr,Vudentz/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,punitvara/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,punitvara/zephyr,punitvara/zephyr,galak/zephyr,mbolivar/zephyr,ldts/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,explora26/zephyr,punitvara/zephyr,nashif/zephyr,explora26/zephyr,zephyriot/zephyr,finikorg/zephyr,finikorg/zephyr,ldts/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,zephyriot/zephyr,galak/zephyr,zephyriot/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,ldts/zephyr,nashif/zephyr,finikorg/zephyr,ldts/zephyr,nashif/zephyr,nashif/zephyr,kraj/zephyr,mbolivar/zephyr,punitvara/zephyr