Reduce bootstrap time in the situation with large properties

[Shawyeok]

What's the purpose of this PR

Reduce bootstrap time in the situation with large properties.

Use test method described in #3800, compare results:

	Baseline	New
	11717ms	599ms
	12755ms	647ms
	12849ms	567ms
	11482ms	627ms
	11903ms	611ms
Stdev	622ms	30ms
Aveage	12141ms	610ms

Which issue(s) this PR fixes:

Fixes #3800

Brief changelog

Reduce bootstrap time in the situation with large properties.

Follow this checklist to help us incorporate your contribution quickly and easily:

• Read the Contributing Guide before making this pull request.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit tests to verify the code.
• Run mvn clean test to make sure this pull request doesn't break anything.
• Update the CHANGES log.

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[Shawyeok]

I have read the CLA Document and I hereby sign the CLA

[codecov-commenter]

Codecov Report

Merging #3816 (c8e839d) into master (622e35a) will increase coverage by 0.16%.
The diff coverage is 87.50%.

@@             Coverage Diff              @@
##             master    #3816      +/-   ##
============================================
+ Coverage     49.93%   50.10%   +0.16%     
- Complexity     2442     2460      +18     
============================================
  Files           482      483       +1     
  Lines         14853    14891      +38     
  Branches       1507     1515       +8     
============================================
+ Hits           7417     7461      +44     
+ Misses         6914     6906       -8     
- Partials        522      524       +2     

Impacted Files	Coverage Δ
...ramework/apollo/core/ApolloClientSystemConsts.java	0.00% <ø> (ø)
...va/com/ctrip/framework/apollo/util/ConfigUtil.java	81.56% <81.25%> (-0.04%)	⬇️
...o/spring/config/CachedCompositePropertySource.java	87.50% <87.50%> (ø)
...ring/boot/ApolloApplicationContextInitializer.java	94.33% <100.00%> (+0.33%)	⬆️
...ork/apollo/spring/config/ConfigPropertySource.java	100.00% <100.00%> (ø)
...apollo/spring/config/PropertySourcesProcessor.java	92.72% <100.00%> (+0.27%)	⬆️
...ervice/service/ReleaseMessageServiceWithCache.java	85.88% <0.00%> (-1.18%)	⬇️
.../apollo/internals/RemoteConfigLongPollService.java	78.31% <0.00%> (+1.20%)	⬆️
.../framework/apollo/spring/property/SpringValue.java	89.47% <0.00%> (+1.75%)	⬆️
... and 2 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 622e35a...c8e839d. Read the comment docs.

[nobodyiam]

Basically it looks good now except for some minor comments, thanks!

[nobodyiam]

Please also update the branch and solve the conflicts in CHANGES.md.

[Shawyeok]

Please also update the branch and solve the conflicts in CHANGES.md.

Done.

[nobodyiam]

LGTM