Add move constructors for string_scalar and struct_scalar

[ttnghia]

This PR adds some move constructors for string_scalar and struct_scalar that accept r-value references to existing buffers. By doing so, the input buffer is moved into the internal buffer of the newly constructed scalars instead of copying.

This also cleans up/rewrites doxygens for scalar.hpp.

Closes #8427.

[davidwendt]

Why are all the comments reformatted?

[ttnghia]

Why are all the comments reformatted?

I just want to enforce aesthetic consistency for them: some comments ended with a period (.) while some others don't. Other (line adjustment) may be due to some explicit reformatting done by my IDE.

[codecov]

Codecov Report

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@@               Coverage Diff               @@
##             branch-21.08    #8428   +/-   ##
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  Coverage                ?   82.95%           
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  Files                   ?      109           
  Lines                   ?    18091           
  Branches                ?        0           
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  Hits                    ?    15008           
  Misses                  ?     3083           
  Partials                ?        0           

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[harrism]

I think secretly this PR is more about adding periods to the comments. :)

I think this is a good addition, just some doc suggestions.

[harrism]

Other (line adjustment) may be due to some explicit reformatting done by my IDE.

Please disable this and just use our mandated clang-format settings. Other than automatic line-wrapping to ensure passing clang-format tests, any reformatting of comments should be done manually and not on every file save or it will make PRs harder to review (and cause more conflicts, e.g. with my in-progress scalar.hpp refactor PR)

I had a hard time getting to the real changes in this PR.

[ttnghia]

Please disable this and just use our mandated clang-format settings. Other than automatic line-wrapping to ensure passing clang-format tests, any reformatting of comments should be done manually and not on every file save or it will make PRs harder to review (and cause more conflicts, e.g. with my in-progress scalar.hpp refactor PR)

I had a hard time getting to the real changes in this PR.

I'm sorry about that. Typically it is disabled, I just accidentally called that this time.

[ttnghia]

Rerun tests.

[ttnghia]

Rerun tests.

[ttnghia]

Rerun tests.

[mythrocks]

LGTM.

(Sorry, I thought I had already approved this PR last week.)

[ttnghia]

@gpucibot merge