Fix defaults documentation of ShapeOptions and TextOptions properties

[0xced]

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Description

Some defaults value documentation were wrong. Also, <para/> was added to make the defaults stand out.

Before this pull request:

After this pull request:

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[codecov]

Codecov Report

Merging #156 (fb98a82) into master (b58a245) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #156   +/-   ##
=======================================
  Coverage   69.87%   69.87%           
=======================================
  Files          88       88           
  Lines        5135     5135           
  Branches     1048     1048           
=======================================
  Hits         3588     3588           
  Misses       1337     1337           
  Partials      210      210           

Flag	Coverage Δ
unittests	69.87% <ø> (ø)

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Impacted Files	Coverage Δ
src/ImageSharp.Drawing/Processing/ShapeOptions.cs	100.00% <ø> (ø)
src/ImageSharp.Drawing/Processing/TextOptions.cs	100.00% <ø> (ø)

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[antonfirsov]

LGTM. Thanks!