Fix more clang and gcc warnings

[marcalff]

Fixes #1649

Changes

Fixed some warnings reported by clang.

-Wnewline-eof
no newline at end of file

-Wc++98-compat-extra-semi
extra ';' outside of a function is incompatible with C++98

-Winconsistent-missing-destructor-override
'~XXX' overrides a destructor but is not marked 'override'

-Wheader-hygiene
using namespace directive in global context in header

-Wunused-parameter
unused parameter

-Wrange-loop-bind-reference

/home/malff/CODE/MARC_GITHUB/opentelemetry-cpp/exporters/otlp/src/otlp_populate_attribute_utils.cc:179:22: error: loop variable 'val' binds to a temporary value produced by a range of type 'const std::vector<bool>' [-Werror,-Wrange-loop-bind-reference]
    for (const auto &val : nostd::get<std::vector<bool>>(value))
                     ^
/home/malff/CODE/MARC_GITHUB/opentelemetry-cpp/exporters/otlp/src/otlp_populate_attribute_utils.cc:179:10: note: use non-reference type 'bool'
    for (const auto &val : nostd::get<std::vector<bool>>(value))
         ^~~~~~~~~~~~~~~~~

Fixed some warnings reported by gcc.

-Werror=missing-field-initializers
missing initializer for member ‘opentelemetry::v1::sdk::trace::SamplingResult::trace_state’

-Werror=unused-variable
unused variable

-Werror=unused-parameter
unused parameter

Added override keywords, and fixed casts to use const_cast.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1658 (65d7557) into main (7724361) will increase coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1658      +/-   ##
==========================================
+ Coverage   84.39%   84.41%   +0.03%     
==========================================
  Files         168      170       +2     
  Lines        5122     5130       +8     
==========================================
+ Hits         4322     4330       +8     
  Misses        800      800              

Impacted Files	Coverage Δ
api/include/opentelemetry/common/kv_properties.h	98.96% <ø> (ø)
...lemetry/context/propagation/composite_propagator.h	100.00% <ø> (ø)
api/include/opentelemetry/trace/context.h	100.00% <ø> (ø)
...ude/opentelemetry/exporters/ostream/common_utils.h	100.00% <ø> (ø)
...clude/opentelemetry/sdk/common/attributemap_hash.h	76.48% <ø> (ø)
...metry/sdk/metrics/aggregation/aggregation_config.h	100.00% <ø> (ø)
...clude/opentelemetry/sdk/metrics/sync_instruments.h	100.00% <ø> (ø)
...ntelemetry/sdk/metrics/view/attributes_processor.h	100.00% <ø> (ø)
...ude/opentelemetry/sdk/metrics/view/view_registry.h	93.75% <ø> (ø)
sdk/include/opentelemetry/sdk/trace/id_generator.h	100.00% <ø> (ø)
... and 11 more

[owent]

LGTM

[esigo]

LGTM
Thanks for the fixes :)