Move oneapi::tbb::concurrent_hash_map heterogeneous extensions from preview

[kboyarinov]

Description

Move heterogeneous overloads for concurrent_hash_map lookup, insert and erase out of preview:

• Remove TBB_PREVIEW_CONCURRENT_HASH_MAP_EXTENSIONS macro around the overloads

• Move tests from tbb folder to conformance

• Remove the documentation from reference

• - git commit message contains appropriate signed-off-by string (see CONTRIBUTING.md for details)

Type of change

Choose one or multiple, leave empty if none of the other choices apply

Add respective label(s) to PR if you have permissions

• bug fix - change which fixes an issue
• new feature - change which adds functionality
• tests - change in tests
• infrastructure - change in infrastructure and CI
• documentation - documentation update

Tests

• added - required for new features and for some bug fixes
• not needed

Documentation

• updated in this PR
• needs to be updated
• not needed

Breaks backward compatibility

• Yes
• No
• Unknown

Notify the following users

List users with @ to send notifications

Other information

[alexey-katranov]

The tests seem slightly simplified, they do not test concurrency and more than one heterogeneous key presence. Surely, it is not a blocker, feel free to commit.