Co-authored-by: Tijana Vislavski Gradina <tijanavg@google.com>

This is a continuation of #2762

Co-authored-by: penmetsaa <penmetsaa@google.com>

* Metadata updates for release 8.12.49
* Update Release Notes refarding new metadata resources

* Revert "Metadata updates for release 8.12.47 (#2754)"

This reverts commit 4f9dbce606.

* Fix carrier and geocoding data file paths

This very minor, trivial and risk free commit fix introduced in 8.12.45 with #2734
error: ignoring return value of function declared with 'warn_unused_result' attribute [-Werror,-Wunused-result]"
Without this fix, I cannot build using clang++13

- Faced link errors stemmed from mismatch of api definitions of absl::node_hash_set. So explicitly mentioned this lib as dependency during linking. This is common case/solution for absl hash set lib's link errors as per community.
- Decided to continued to have wrapper (stringutil), so that in future it's easy if we decided to change implementation; client code is safe. Changed most of the implementations & data structures in stringutil, to use abseil stuffs more.
- Though absl::string_view is suitable for most cases where we want immutable/read-only string structures, limiting to stringutil apis, not changing public API signatures (even though no compliance issue); reason: reduce dependency on abseil libs.
- Abseil specific changes done:
    - std::set => absl::node_hash_set
    - std::map => absl::node_hash_map
    - Using absl alternatives for “SplitStringUsing” API and “StringHolder” class impl.
    - Replaced manual impl of prefix and suffix checks with absl::StartsWith() and absl::EndsWith.
    - Similarly used absl::StrReplaceAll, absl::StrCat, absl::StrAppend where possible; and for type conversion apis.
- Note: Tried applying parameter packs to replace manually written duplicate ```StrCat``` apis (for accommodating more number of parameters of same type), but it did not go well when different type arguments passed. Eg char, int types to be converted to StringHolder; faced constructor implicit conversion issues.

* Accelerate conversion from integer to string, using abseil StrCat and StrAppend function

* minor code simplification

Keep track of whether unicode strings were created from valid UTF-8 and
use this to abort operations that use these strings later.

Typically, this is done by returning an empty string when a modified
string is being produced, since an empty string is never a valid phone
number.

@API updates:
- Migrating from associative containers to more performant types. Eg: map to absl::btree_map.
- Synchronise the write access to map "AreaCodeMaps" using absl::Mutex locking api.
- Use more of absl:strings packages like absl::StrReplaceAll

@Build updates:
- To build (CMake) against absl packages, the minimum version of compiler is CPP11+, whereas earlier we are not mandating this.
- We are upgrading CMAKE version also to automate building the external absl packages.

The change is announced. Please report issues in case of any breakages.
https://issuetracker.google.com/issues?q=componentid:192347%20555

Merged as part of b/207106531

Earlier, AYTF is adding additional CC when returning unformatted result - for cases where the input digits are dropped for formatting. Eg: MX case: "+5213314010666" => "+52 +5213314010666". b/183053929

Now we. are proactively ensuring that no formatting is applied, where a format is chosen that would otherwise have led to some digits being dropped.

Why the input digits are dropped:
- In MX, the mobile token (1) is no more used, so when it is present in input, the formatted result should not contain it.
- However when AYTF, we should not be removing the input digits on the fly.
- More details in cl/373115460 and b/183053929