TypeSafeMatching no longer iterates over class methods inefficiently

[j-baker]

Fixes #2723.

Class.getMethods is an inefficient method call which is being called on
each mock invocation. It ends up constructing new Method objects for
each method on the class, and this can dominate the overall performance
of Mockito mocks. This commit caches the result of the computation.

Once concern is that this change uses some static state. I considered:

• Instance state - based on where this type is constructed it seemed
  like it'd be a big imposition on code readability elsewhere.
• Weakly referenced map. Mockito has a type for this, but the
  constructor of that type produces a Thread with which to clean up.

Both of these seemed like overkill compared to the overhead expected
in the real world (which should be on the order of a few kilobytes of
RAM at most).

Checklist

• Read the contributing guide
• PR should be motivated, i.e. what does it fix, why, and if relevant how
• If possible / relevant include an example in the description, that could help all readers
  including project members to get a better picture of the change
• Avoid other runtime dependencies
• Meaningful commit history ; intention is important please rebase your commit history so that each
  commit is meaningful and help the people that will explore a change in 2 years
• The pull request follows coding style
• Mention Fixes #<issue number> in the description if relevant
• At least one commit should mention Fixes #<issue number> if relevant

[j-baker]

I saw you triggered CI and it failed. I've edited the PR subsequently and it certainly passes locally...

[codecov-commenter]

Codecov Report

Merging #2729 (c7312d3) into main (70c1fe9) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #2729      +/-   ##
============================================
+ Coverage     86.27%   86.28%   +0.01%     
  Complexity     2795     2795              
============================================
  Files           317      317              
  Lines          8395     8402       +7     
  Branches       1046     1049       +3     
============================================
+ Hits           7243     7250       +7     
  Misses          879      879              
  Partials        273      273              

Impacted Files	Coverage Δ
.../mockito/internal/invocation/TypeSafeMatching.java	91.66% <100.00%> (+3.43%)	⬆️

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[TimvdLippe]

Nice fix, thanks!