fix: incorrectly placed matrix delimiters

[muzimuzhi]

Motivation for this change

See analysis #1102 (comment).

With previous fix 438758d for similar problem #126 as reference, code change is easy to understand. To better testing, \AssertPointEquals[<tolerance>]{<point>}{<point>}, \TikzGetOnePoint{<point>}{<macro>} and some small helping commands are added to pgf-regression-test.tex.

(It's only my personal preference to try to avoid dumping boxes and writing hundreds of lines of puzzling incantations/backend-dependent specials to log. Box-content-based and PDF-based tests are more accurate, but the generated test files (.tlg and .pvt ) is harder to read.)

Fixes #1102

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