- taken from: llvm-mirror/libcxx@78d6a77

- add missing empty and max_size methods required by tests

string_view: implement access API and port libcxx tests

- change implementation to use pmem::obj::string_view

- add missing functions: front, back
- extend declarations by constexpr keyword

- taken from: llvm-mirror/libcxx@78d6a77

Merge changes from stable-1.11 to master

add concurrent_hash_map concurrent erase defrag test

ref: #892

cmake: add ccache support

Move Coverity job to GHA

On my not-so-fast NUC it improves build time:

clean build without ccache (and first build with ccache):
real	6m15.062s
user	19m45.633s
sys	1m48.421s

second clean build with ccache:
real	0m48.836s
user	1m48.793s
sys	0m35.407s

It's not needed for CI, as builds are done in containers and do not share
ccache anyway

add range methods to basic_string

radix_tree: fix internal find

string_view: add relational operators for string_view class

- add -Ob3 flag to avoid C1064 error in Windows environment

- extend tests to test also wchar_t type

- port libcxx tests to use pmem::obj::string_view class

- taken from: llvm-mirror/libcxx@78d6a77

- add missing relational operators for string_view

Fix comparison between n->byte and key.size(). When using pmem::obj::string
or inline_string the behavior was ok (since we always have null terminator
at the end), but we technically access out-of-range memory which can cause
asserts in string_view operator[].

examples: update min cmake version to 3.4

fix default bytes_view in radix_tree

radix_tree improvements

docker: fix auto docs generating - force clean dir

use try_emplace instead of emplace

it's required for new branches, where target directory does not exist yet.

Merge changes from stable 1.11 to master

in examples using 'include' command - it also uses 'CheckIncludeFile'
which (in CMake <=3.3) worked only with set project language (CXX in this case),
and some included files are supposed to be checked with C lang, too.

With help of: https://github.com/nlohmann/cmake_min_version

CI: fix GHA docs' job - use branches names not tags

update Fedora image for doc job

Radix tree assing val fix