dEQP has data files that live in several directories within dEQP's
source tree. For example, GLES3 has data files that live within:

data/gles3/data/
external/graphicsfuzz/data/gles3/

However, we can only tell dEQP about a single data directory during
initialization of dEQP. To get around this, we are manually copying all
of the necessary data files to the output generated files directory and
pointing dEQP to this single directory. This also helps us solve a
second problem related to the paths that dEQP uses when accessing
graphicsfuzz data files.

For the graphicsfuzz tests, dEQP will attempt to open the necessary
shaders by accessing them with the path:

data/gles3/graphicsfuzz/

However, those files would normally live at the path that matches their
location within the source tree:

external/graphicsfuzz/data/gles3/graphicsfuzz/

As part of the manual copy of these data files, we are also able to
strip the extra 'external/graphicsfuzz/' portion of the path.

Bug: angleproject:2322
Test: dEQP
Change-Id: Ibc96442c221485e2f246890fa8fe51f090c5e222
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1881759
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>