Fix sdk/log record attr value limit

[MrAlias]

Fix #6004

Copy of #5997

Correctness

From the OTel specification:

• set an attribute value length limit such that for each attribute value:
  • if it is a string, if it exceeds that limit (counting any character in it as 1), SDKs MUST truncate that value, so that its length is at most equal to the limit...

Our current implementation truncates on number of bytes not characters.

Unit tests are added/updated to validate this fix and prevent regressions.

Performance

goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/log
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
                        │ commit-e9c7aac2(old).txt │       commit-878043b9(new).txt       │
                        │          sec/op          │    sec/op     vs base                │
Truncate/Unlimited-8                 0.8323n ±  3%   0.7367n ± 3%  -11.49% (p=0.000 n=10)
Truncate/Zero-8                       1.923n ± 32%    1.359n ± 2%  -29.34% (p=0.000 n=10)
Truncate/Short-8                    14.6050n ±  4%   0.8785n ± 1%  -93.98% (p=0.000 n=10)
Truncate/ASCII-8                      8.205n ±  2%    3.601n ± 7%  -56.12% (p=0.000 n=10)
Truncate/ValidUTF-8-8                11.335n ±  1%    7.206n ± 1%  -36.43% (p=0.000 n=10)
Truncate/InvalidUTF-8-8               58.26n ±  1%    36.61n ± 1%  -37.17% (p=0.000 n=10)
Truncate/MixedUTF-8-8                 81.16n ±  1%    52.30n ± 1%  -35.56% (p=0.000 n=10)
geomean                               10.04n          4.601n       -54.16%

                        │ commit-e9c7aac2(old).txt │      commit-878043b9(new).txt       │
                        │           B/op           │    B/op     vs base                 │
Truncate/Unlimited-8                  0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/Zero-8                       0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/Short-8                      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/ASCII-8                      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/ValidUTF-8-8                 0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/InvalidUTF-8-8               16.00 ± 0%     16.00 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/MixedUTF-8-8                 32.00 ± 0%     32.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean                                          ²               +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                        │ commit-e9c7aac2(old).txt │      commit-878043b9(new).txt       │
                        │        allocs/op         │ allocs/op   vs base                 │
Truncate/Unlimited-8                  0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/Zero-8                       0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/Short-8                      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/ASCII-8                      0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/ValidUTF-8-8                 0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/InvalidUTF-8-8               1.000 ± 0%     1.000 ± 0%       ~ (p=1.000 n=10) ¹
Truncate/MixedUTF-8-8                 1.000 ± 0%     1.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                                          ²               +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.2%. Comparing base (58fdf2a) to head (878043b).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6032   +/-   ##
=====================================
  Coverage   82.2%   82.2%           
=====================================
  Files        273     273           
  Lines      23647   23674   +27     
=====================================
+ Hits       19449   19476   +27     
  Misses      3851    3851           
  Partials     347     347           

see 1 file with indirect coverage changes