api: use easyjson and context in regions interface (#6838)

[ti-chi-bot]

This is an automated cherry-pick of #6838

What problem does this PR solve?

Issue Number: Close #6835

What is changed and how does it work?

1. reduce half memory and cpu usage
2. server stop solving when the client stop

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

1. bench
   go test -benchmem -run=^$ -bench ^BenchmarkGetRegions$ github.com/tikv/pd/server/api -benchtime=30s

	times	ns/op	B/op	allocs/op
default	12	2964076204	1153885878	4253342
default	12	2985435560	1271459127	4261952
default	12	2994243983	1241259906	4255758
jsoniter	15	2492527400	2384667309	4044502
jsoniter	18	2428125878	2545873184	4018365
jsoniter	18	2207472486	2214775903	3925291
easyjson	26	1381140866	803330238	3582216
easyjson	28	1339109264	786423035	3564425
easyjson	26	1370970701	801957518	3575059
this pr(c501fd8)	24	1386651999	789385029	3577663
this pr(c501fd8)	24	1512373970	814244526	3632067
this pr(c501fd8)	26	1455024327	794162807	3603735
this pr(2b1ab88)	31	1343236075	558050128	3568320
this pr(2b1ab88)	30	1249315290	551981506	3534328
this pr(2b1ab88)	31	1316071881	544873733	3557758

	ns/op	ns diff	B/op	Bytes diff	allocs/op	alloc diff
default	2981251916		1222201637		4257017
jsoniter	2376041921	-20%	2381772132	95%	3996053	-6%
easyjson	1363740277	-54%	797236930	-35%	3573900	-16%
this pr(c501fd8)	1451350099	-51%	799264121	-35%	3604488	-15%
this pr(2b1ab88)	1302874415	-56%	551635122	-55%	3553468	-17%

2. kill and ensure the goroutine exit
   client: curl -s -o /dev/null http://192.168.8.88:2379/pd/api/v1/regions and ctrl-c
   server: goroutine exit

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HuSharp
• bufferflies

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[AndreMouche]

@lhy1024 could you please take a look? /scripts/embed-dashboard-ui.sh failed

[lhy1024]

@AndreMouche It is an enhancement, I think we should provide a hotfix rather than pick it to 6.5.

[lhy1024]

@AndreMouche I fix the conflict, but I am not sure whether pick it to other branches. cc @nolouch @niubell

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.03% ⚠️

Comparison is base (3a19dec) 75.59% compared to head (d8ac207) 75.57%.
Report is 1 commits behind head on release-6.5.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-6.5    #6855      +/-   ##
===============================================
- Coverage        75.59%   75.57%   -0.03%     
===============================================
  Files              328      329       +1     
  Lines            33199    33595     +396     
===============================================
+ Hits             25097    25389     +292     
- Misses            5947     6028      +81     
- Partials          2155     2178      +23     

Flag	Coverage Δ
unittests	75.57% <66.66%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
server/api/region_easyjson.go	62.01% <62.01%> (ø)
server/config/store_config.go	80.43% <71.42%> (-1.18%)	⬇️
server/api/region.go	70.45% <83.87%> (+2.24%)	⬆️
server/cluster/cluster.go	81.58% <100.00%> (+0.02%)	⬆️
server/core/test_util.go	84.67% <100.00%> (+1.20%)	⬆️
server/schedule/waiting_operator.go	97.36% <100.00%> (ø)

... and 21 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
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[lhy1024]

/merge

[ti-chi-bot]

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: d8ac207