Make minor C++ docstring adjustments

[EricCousineau-TRI]

As part of #13461 (but also good as a standalone)

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This change is 

[EricCousineau-TRI]

+@jwnimmer-tri for both reviews, please.
+(status: single reviewer ok)

Reviewable status: LGTM missing from assignee jwnimmer-tri(platform) (waiting on @jwnimmer-tri)

[jwnimmer-tri]

both.

Reviewed 7 of 7 files at r1.
Reviewable status: 1 unresolved discussion (waiting on @EricCousineau-TRI)

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solvers/test/semidefinite_program_examples.h, line 90 at r1 (raw file):

 * s.t [x0 x1] is psd
 *     [x1 x0]
 *

Both of these changed lines seem worse to me. We now have a weird blank line inbetween the exposition of the mathematical program, inconsistent within this definition itself, and different than its peers higher up in the file, etc.

[EricCousineau-TRI]

Reviewable status: 1 unresolved discussion (waiting on @jwnimmer-tri)

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solvers/test/semidefinite_program_examples.h, line 90 at r1 (raw file):

Previously, jwnimmer-tri (Jeremy Nimmer) wrote…

Both of these changed lines seem worse to me. We now have a weird blank line inbetween the exposition of the mathematical program, inconsistent within this definition itself, and different than its peers higher up in the file, etc.

Done.

[jwnimmer-tri]

-(status: single reviewer ok)

+@hongkai-dai for feature review of semidefinite_program_examples.h (only), please.

Reviewed 1 of 1 files at r2.
Reviewable status: LGTM missing from assignee hongkai-dai (waiting on @hongkai-dai)

[hongkai-dai]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all discussions resolved, LGTM from assignees jwnimmer-tri(platform),hongkai-dai