Doxygen: Hide friend declarations in dox.

Merge pull request #8519 from cmonr/rollup ...

Rollup PR - UK Docathon pt1

Merge pull request #8003 from Taiki-San/patch-2 ...

Leverage the simplification of the IPv6 parsing primitive

Merge pull request #8332 from SenRamakri/sen_RefactorFaultHandler ...

Refactoring fault handler implementation

Merge pull request #8478 from JarkkoPaso/fhss_timer_dev ...

Fhss timer dev

Merge pull request #8515 from theotherjimmy/dupe-json ...

Merge duplicate keys in JSON.

Merge pull request #8505 from SeppoTakalo/continue_socket_tests ...

Continue Socket and WiFi tests even on test failure.

Merge pull request #8474 from naveenkaje/NRF_RTS_Followon_Fix ...

NRF52 : Fix UART RTS initialization

Merge branch 'mbed_rtc_time_example_fix' of ssh://github.com/mprse/mbed-os into rollup

Merge branch 'span-doc' of ssh://github.com/pan-/mbed into rollup

Merge branch 'doc-fix-i2c_slave' of ssh://github.com/paul-szczepanek-arm/mbed-os into rollup

Merge branch 'doc-fix-spi_slave' of ssh://github.com/paul-szczepanek-arm/mbed-os into rollup

Merge branch 'conbra01/docaton_networksocket' of ssh://github.com/ConradBraam/mbed-os into rollup

Merge branch 'docs_update-eventflags' of ssh://github.com/fkjagodzinski/mbed-os into rollup

Merge pull request #8430 from theamirocohen/block_device_general_tests ...

Block device general tests

Edit EventFlags.h ...

Make minor copy edits to existing text.

Space optimization to fault handlers

Moving fault handlers under cmsis

Mbed Fault Handler was originally placed under rtos folder because of its dependency on some of the RTX data structures for capturing the thread info. But with the new error handling in place thread info collection on hardfaults has been moved to Mbed_error handler. There is no point for fault handler implementation to exist under rtos and can be used for RTOS-less builds as well. So moving under platform folder. Also removing some references to RTX data structs like osRtxInfo from fault handler implementation.

Merge pull request #8485 from NXPmicro/feature-qspi-kinetis ...

Feature qspi kinetis

Merge pull request #7966 from pingdan32/fix_nrf52_total_link ...

nrf52-ble: fix total links count

Add comma to SocketAddress.h ...

Add comma to existing text.

Merge duplicate keys in JSON. ...

### Description

I would love to make this an error, but we have had a duplicate key in
`targets.json` for a while now. Instead, we're merging in a semi-smart way.
This will allow you to have things like `"target.features_add"` twice, and
both will take affect.

### Pull request type

    [x] Fix
    [ ] Refactor
    [ ] Target update
    [ ] Functionality change
    [ ] Docs update
    [ ] Test update
    [ ] Breaking change

Merge pull request #8369 from u-blox/ublox-cellular-target ...

Cellular: UBLOX_C030_R410M cellular target add

Merge pull request #8352 from offirko/offir-mbed-qspif ...

QSPI SFDP Flash Block Device

NRF52 : Fix UART RTS initialization ...

The preprocessor based macro check #if evaluates all
enums as 0 and hence the code does not get compiled.
Since move this to a runtime check where the pin variable
can be correctly evaluated.

Delete mbed_overrides.c as it has a target specific mbed_sdk_init() to
resolve linking problem.

This is a follow on patch to:
https://github.com/ARMmbed/mbed-os/pull/8046

Merge pull request #8489 from tkem/fix/uartserial-include ...

Clean up UARTSerial.cpp includes.

Edit SPISlave.h ...

Make minor edits to existing text.

Copy edit I2CSlave.h ...

Make minor copy edits.

Merge pull request #8495 from bridadan/patch_add_linker_line ...

Adding file type for linker script arg in make script