Pool Binders like we do Parsers

[jakebailey]

This is a very good binder win.

goos: linux
goarch: amd64
pkg: github.com/microsoft/typescript-go/internal/binder
cpu: Intel(R) Core(TM) i9-10900K CPU @ 3.70GHz
                                                     │   old.txt    │               new.txt                │
                                                     │    sec/op    │    sec/op     vs base                │
Bind/empty.ts-20                                       417.6n ± 25%   280.0n ± 21%  -32.94% (p=0.000 n=10)
Bind/checker.ts-20                                     18.46m ±  4%   17.22m ±  1%   -6.74% (p=0.000 n=10)
Bind/dom.generated.d.ts-20                             7.713m ±  3%   7.440m ±  2%   -3.54% (p=0.002 n=10)
Bind/Herebyfile.mjs-20                                 307.5µ ±  2%   302.0µ ±  4%        ~ (p=0.353 n=10)
Bind/jsxComplexSignatureHasApplicabilityError.tsx-20   156.6µ ±  4%   153.1µ ±  3%   -2.24% (p=0.043 n=10)
geomean                                                310.0µ         277.9µ        -10.35%

                                                     │   old.txt    │               new.txt                │
                                                     │     B/op     │     B/op      vs base                │
Bind/empty.ts-20                                         432.0 ± 0%     192.0 ± 0%  -55.56% (p=0.000 n=10)
Bind/checker.ts-20                                     7.206Mi ± 0%   7.206Mi ± 0%   -0.00% (p=0.000 n=10)
Bind/dom.generated.d.ts-20                             4.873Mi ± 0%   4.873Mi ± 0%   -0.01% (p=0.000 n=10)
Bind/Herebyfile.mjs-20                                 174.2Ki ± 0%   173.8Ki ± 0%   -0.21% (p=0.000 n=10)
Bind/jsxComplexSignatureHasApplicabilityError.tsx-20   114.8Ki ± 0%   114.4Ki ± 0%   -0.31% (p=0.000 n=10)
geomean                                                198.8Ki        168.9Ki       -15.06%

                                                     │   old.txt   │               new.txt               │
                                                     │  allocs/op  │  allocs/op   vs base                │
Bind/empty.ts-20                                        3.000 ± 0%    2.000 ± 0%  -33.33% (p=0.000 n=10)
Bind/checker.ts-20                                     13.69k ± 0%   13.69k ± 0%   -0.01% (p=0.000 n=10)
Bind/dom.generated.d.ts-20                             14.68k ± 0%   14.68k ± 0%   -0.01% (p=0.000 n=10)
Bind/Herebyfile.mjs-20                                  344.0 ± 0%    342.0 ± 0%   -0.58% (p=0.000 n=10)
Bind/jsxComplexSignatureHasApplicabilityError.tsx-20    280.0 ± 0%    278.0 ± 0%   -0.71% (p=0.000 n=10)
geomean                                                 565.9         520.5        -8.03%

[jakebailey]

I was previously far too clever; this was actually a bad idea because we were keeping every Binder alive longer than it needed to be. Reusing the Binders caused a race for that reason, since we were taking an interior pointer.