RTOS API for bare metal ...

Provide partial RTOS API for bare metal builds - things that
can be done in a single threaded environment.

Allows more code to work in both RTOS and bare metal builds without
change, and in particular gives easy access to the ability to
efficiently wait for something occurring in interrupt.

Available in bare-metal:
* ThisThread
* osThreadFlagsSet to set flags on main thread (can be set from IRQ)
* EventFlags (can be set from IRQ)
* Semaphores (can be released from IRQ)
* Mutex (dummy implementation)

Not useful:
* ConditionVariable (could only be signalled from 2nd thread)
* RtosTimer (calls in a second thread context)
* Thread

Unimplemented:
* Mail, Queue, MemoryPool

Possible future work:
* ConditionVariableCS to act as IRQ signalled ConditionVariable

rtos/mbed_lib.json: Correct indents

Merge pull request #10855 from OpenNuvoton/nuvoton_idle_stack_underflow_debug ...

Nuvoton: Fix idle thread stack underflow in debug build

Allow target or application level definition of extra TICKLESS stack size ...

Adding a check to let application or target force increase idle thread
stack size.

[Nuvoton] Fix idle thread stack underflow in debug build ...

In rtos/mbed_lib.json:
Enlarge idle-thread-stack-size-debug-extra for all Nuvoton targets.

In rtos/TARGET_CORTEX/mbed_rtx_conf.h:
MBED_DEBUG also must be defined for this configuration parameter to take effect.

Increase background stack size to fix overflows with debug profile

Increase background stack size to fix overflows ...

On platforms using both tickless and the low power ticker wrapper
so much of the background stack is used that it overflows. To
ensure the background thread's stack doesn't overflow increase this
size by 256 bytes when tickless is enabled. Worst case usage
on the NUCLEO_F476RG was recorded at 656 when tickless is
turned on so this increased size should safely prevent overflows.

Merge pull request #8039 from c1728p9/stack_size_framework ...

Add framework for configuring boot stack size

Replace macros with config options ...

Add a config option for the following values:
MBED_SYS_STATS_ENABLED
MBED_STACK_STATS_ENABLED
MBED_CPU_STATS_ENABLED
MBED_HEAP_STATS_ENABLED
MBED_THREAD_STATS_ENABLED
MBED_CONF_APP_MAIN_STACK_SIZE
MBED_CONF_APP_TIMER_THREAD_STACK_SIZE
MBED_CONF_APP_IDLE_THREAD_STACK_SIZE
MBED_CONF_APP_THREAD_STACK_SIZE

To maintain backwards compatibility inside the RTOS both
APP and RTOS config values can be used.

Add framework for configuring boot stack size ...

Add the target config option "boot-stack-size" which is passed to the
linker as the define "MBED_BOOT_STACK_SIZE" so the linker can
adjust the stack accordingly. On mbed 2 the boot stack becomes the
main stack after boot.  On mbed 5 the boot stack becomes the
ISR stack after boot. Because of these different uses  the stack size
for mbed 2 is set to 4K by default while on mbed 5 it is set to 1k.

Additionally, the NRF5X family requires a larger interrupt stack size
due to the softdevice so the size  is increased to 2k on mbed 5 builds.

Add _RTX_ define where it's needed and used

RTOS - add config mbed_lib.json file ...

Defines that rtos is present, this resolves in the macro:
"MBED_CONF_RTOS_PRESENT=1"