test: Move bug cases to sub-directories

The test runner now recursively scans sub-directories.
Use this for sensibly structuring our test files.

test/bug/tint/###.[wgsl,spvasm] files refer to bugs filed at:
crbug.com/tint/###

Change-Id: I9b4d8d134c8494b0f48c8656f3bf694f76d5303f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51221
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: David Neto <dneto@google.com>
diff --git a/test/bug_tint_749.spvasm b/test/bug/tint/749.spvasm
similarity index 100%
rename from test/bug_tint_749.spvasm
rename to test/bug/tint/749.spvasm
diff --git a/test/bug_tint_749.spvasm.expected.hlsl b/test/bug/tint/749.spvasm.expected.hlsl
similarity index 100%
rename from test/bug_tint_749.spvasm.expected.hlsl
rename to test/bug/tint/749.spvasm.expected.hlsl
diff --git a/test/bug_tint_749.spvasm.expected.msl b/test/bug/tint/749.spvasm.expected.msl
similarity index 100%
rename from test/bug_tint_749.spvasm.expected.msl
rename to test/bug/tint/749.spvasm.expected.msl
diff --git a/test/bug_tint_749.spvasm.expected.spvasm b/test/bug/tint/749.spvasm.expected.spvasm
similarity index 100%
rename from test/bug_tint_749.spvasm.expected.spvasm
rename to test/bug/tint/749.spvasm.expected.spvasm
diff --git a/test/bug_tint_782.wgsl b/test/bug/tint/782.wgsl
similarity index 100%
rename from test/bug_tint_782.wgsl
rename to test/bug/tint/782.wgsl