Removes reflection from RouteContext to reduce allocations (envoyproxy#6820)

* bench: adds APIToXDS bench & small opt

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

* no refect

goos: darwin
goarch: arm64
pkg: github.com/envoyproxy/gateway/test/gobench
cpu: Apple M1 Pro
                          │   old.txt    │               new.txt               │
                          │    sec/op    │   sec/op     vs base                │
GatewayAPItoXDS/small-10    881.2µ ±  7%   803.4µ ± 1%   -8.82% (p=0.000 n=10)
GatewayAPItoXDS/medium-10   4.130m ± 26%   2.959m ± 4%  -28.36% (p=0.000 n=10)
GatewayAPItoXDS/large-10     5.375 ±  2%    4.553 ± 1%  -15.28% (p=0.000 n=10)
geomean                     26.94m         22.12m       -17.90%

                          │   old.txt    │               new.txt                │
                          │     B/op     │     B/op      vs base                │
GatewayAPItoXDS/small-10    507.2Ki ± 0%   492.9Ki ± 0%   -2.83% (p=0.000 n=10)
GatewayAPItoXDS/medium-10   2.545Mi ± 7%   1.954Mi ± 2%  -23.21% (p=0.000 n=10)
GatewayAPItoXDS/large-10    2.832Gi ± 0%   2.831Gi ± 0%        ~ (p=0.529 n=10)
geomean                     15.40Mi        13.97Mi        -9.31%

                          │   old.txt   │               new.txt               │
                          │  allocs/op  │  allocs/op   vs base                │
GatewayAPItoXDS/small-10    8.328k ± 0%   8.017k ± 0%   -3.73% (p=0.000 n=10)
GatewayAPItoXDS/medium-10   39.45k ± 6%   29.74k ± 2%  -24.60% (p=0.000 n=10)
GatewayAPItoXDS/large-10    38.75M ± 0%   38.71M ± 0%   -0.11% (p=0.000 n=10)
geomean                     233.5k        209.8k       -10.16%

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

* removes garbage

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

* more tests

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

* more tests

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

---------

Signed-off-by: Takeshi Yoneda <t.y.mathetake@gmail.com>

Author: mathetake

internal/gatewayapi/backendtrafficpolicy.go

@@ -48,7 +48,7 @@ func (t *Translator) ProcessBackendTrafficPolicies(resources *resource.Resources
 	routeMap := map[policyTargetRouteKey]*policyRouteTargetContext{}
 	for _, route := range routes {
 		key := policyTargetRouteKey{
-			Kind:      string(GetRouteType(route)),
+			Kind:      string(route.GetRouteType()),
 			Name:      route.GetName(),
 			Namespace: route.GetNamespace(),
 		}