Java: Add model for CharArrayWriter.toString().

[aschackmull]

Found by speculative flow.

[github-actions[bot]]

:warning: The head of this PR and the base branch were compared for differences in the framework coverage reports. The generated reports are available in the artifacts of this workflow run. The differences will be picked up by the nightly job after the PR gets merged.

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java

Generated file changes for java

• Changes to framework-coverage-java.rst:

-    Java Standard Library,``java.*``,10,4284,259,99,,9,,,26
+    Java Standard Library,``java.*``,10,4285,259,99,,9,,,26
-    Totals,,312,25170,2635,404,16,128,33,1,409
+    Totals,,312,25171,2635,404,16,128,33,1,409

• Changes to framework-coverage-java.csv:

- java.io,66,1,256,,,,,,,,,22,,,,,,,,,,,,,,,44,,,,,,,,,,,,,,,,,,,,,,1,,249,7
+ java.io,66,1,257,,,,,,,,,22,,,,,,,,,,,,,,,44,,,,,,,,,,,,,,,,,,,,,,1,,250,7