Improve 'search' message to add context

[vladanost]

This PR is referencing issue #2338
I have updated the Inserter search message to read "Search blocks" to be identical to the screen reader text message above it.

[karmatosed]

I still wonder how discoverable the word blocks is for people that don't know about blocks. In saying that 'Search blocks' is better than we currently have. I would be keen on more human language such as 'Find a block' or 'Search for a block' over 'Search blocks'. Could you iterate on that maybe?

[vladanost]

I went for 'Find a block'. It's shorter than 'Search for a block' and feels better to me than 'Search blocks'.

[codecov]

Codecov Report

Merging #2692 into master will increase coverage by 0.66%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2692      +/-   ##
==========================================
+ Coverage   33.16%   33.82%   +0.66%     
==========================================
  Files         182      189       +7     
  Lines        5530     5661     +131     
  Branches      963      988      +25     
==========================================
+ Hits         1834     1915      +81     
- Misses       3130     3171      +41     
- Partials      566      575       +9

Impacted Files	Coverage Δ
editor/inserter/menu.js	49.59% <ø> (+1.18%)	⬆️
components/popover/index.js	88.04% <0%> (-4.92%)	⬇️
editor/selectors.js	94.73% <0%> (-1.67%)	⬇️
editor/sidebar/post-visibility/index.js	45.23% <0%> (-0.92%)	⬇️
blocks/api/parser.js	98.14% <0%> (-0.04%)	⬇️
components/form-file-upload/index.js	71.42% <0%> (ø)	⬆️
components/popover/detect-outside.js	25% <0%> (ø)	⬆️
editor/modes/visual-editor/block-list.js	0% <0%> (ø)	⬆️
editor/modes/visual-editor/block-crash-boundary.js	0% <0%> (ø)	⬆️
editor/writing-flow/index.js	0% <0%> (ø)	⬆️
... and 24 more

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[karmatosed]

I think keeping it as Search is better for translation, find doesn't have the same context.