backend: stop allocating ValueDefinitions

[mathetake]

goos: darwin
goarch: arm64
pkg: github.com/tetratelabs/wazero
                      │  old.txt   │             new.txt              │
                      │   sec/op   │   sec/op    vs base              │
Compilation/wazero-10   1.536 ± 1%   1.535 ± 0%       ~ (p=0.589 n=6)
Compilation/zig-10      3.405 ± 1%   3.411 ± 0%       ~ (p=0.240 n=6)
Compilation/zz-10       14.03 ± 0%   14.05 ± 0%       ~ (p=0.310 n=6)
geomean                 4.186        4.190       +0.09%

                      │   old.txt    │              new.txt               │
                      │     B/op     │     B/op      vs base              │
Compilation/wazero-10   273.4Mi ± 0%   257.4Mi ± 0%  -5.84% (p=0.002 n=6)
Compilation/zig-10      594.7Mi ± 0%   592.2Mi ± 0%  -0.42% (p=0.002 n=6)
Compilation/zz-10       532.4Mi ± 0%   525.7Mi ± 0%  -1.26% (p=0.002 n=6)
geomean                 442.4Mi        431.2Mi       -2.53%

                      │   old.txt   │              new.txt              │
                      │  allocs/op  │  allocs/op   vs base              │
Compilation/wazero-10   485.3k ± 0%   485.3k ± 0%       ~ (p=0.699 n=6)
Compilation/zig-10      275.5k ± 0%   275.6k ± 0%       ~ (p=0.394 n=6)
Compilation/zz-10       626.9k ± 0%   627.0k ± 0%       ~ (p=0.394 n=6)
geomean                 437.6k        437.7k       +0.03%

#2182