Add epsilon to float comparison

Adds an epsilon when comparing float values in
conformance/extensions/webgl-depth-texture.html. As-is, it is possible
for tests to fail with output such as:

At 2,0, expected within [0.2,0.6], was 0.600
FAIL At 2,0, expected within [0.2,0.6], was 0.600

sdk/tests/conformance/extensions/webgl-depth-texture.html

@@ -349,7 +349,7 @@
                     const eMax = expectedMax[t];
                     let func = testPassed;
                     const text = `At ${xx},${yy}, expected within [${eMin},${eMax}], was ${was.toFixed(3)}`
-                    if (was <= eMin || was >= eMax) {
+                    if (was <= eMin - eps || was >= eMax + eps) {
                         func = testFailed;
                     }
                     func(text);