Rename QuicheTest implementation to QuicheTestImpl.

This is for consistency with the rest of QUICHE platform, and will also allow
moving QuicheTest (the API, not the impl) from the top level namespace to
quiche::test:

quiche::test::QuicheTest -> quiche::test::QuicheTestImpl (this CL)
::QuicheTest -> quiche::test::QuicheTest (future CL).

Unfortunately this means that after this CL temporarily there will be no
quiche::test::QuicheTest, hence the change in spdy_framer_test.cc that will need
to be reverted when QuicheTest is moved to quiche::test namespace.

To roll this to Envoy, this will require s/QuicheTest/QuicheTestImpl/ at
https://github.com/envoyproxy/envoy/blob/633d190b31ad954fd9250639087ba9772b42df12/test/common/quic/platform/quiche_test_impl.h#L30

To roll this to Chromium, this will require s/QuicheTest/QuicheTestImpl/ at
https://source.chromium.org/chromium/chromium/src/+/main:net/third_party/quiche/overrides/quiche_platform_impl/quiche_test_impl.h;l=20;drc=ea4fa1900a488bdc0c65d6147f2700b08c752d82

PiperOrigin-RevId: 445393094

quiche/common/platform/api/quiche_test.h

diff --git a/quiche/common/platform/api/quiche_test.h b/quiche/common/platform/api/quiche_test.h
index afc298a..b707385 100644
--- a/quiche/common/platform/api/quiche_test.h
+++ b/quiche/common/platform/api/quiche_test.h
@@ -7,7 +7,7 @@
 
 #include "quiche_platform_impl/quiche_test_impl.h"
 
-using QuicheTest = quiche::test::QuicheTest;
+using QuicheTest = quiche::test::QuicheTestImpl;
 
 template <class T>
 using QuicheTestWithParam = quiche::test::QuicheTestWithParamImpl<T>;

quiche/spdy/core/spdy_framer_test.cc

diff --git a/quiche/spdy/core/spdy_framer_test.cc b/quiche/spdy/core/spdy_framer_test.cc
index 0f599fc..29676ed 100644
--- a/quiche/spdy/core/spdy_framer_test.cc
+++ b/quiche/spdy/core/spdy_framer_test.cc
@@ -2935,7 +2935,7 @@
   EXPECT_FALSE(frame_it.HasNextFrame());
 }
 
-class SpdyControlFrameIteratorTest : public quiche::test::QuicheTest {
+class SpdyControlFrameIteratorTest : public QuicheTest {
  public:
   SpdyControlFrameIteratorTest() : output_(output_buffer, kSize) {}