util/sh: strip quotes when splitting build parameters

[davidpavlovschi]

SplitParameters kept quoted sequences together but left the quotes in place, so a config with flags: -a -tags 'netgo static_build' passed the literal argument 'netgo static_build' to go build. Double quotes were not recognized at all, so -gcflags="all=-N -l" split into two arguments.

This replaces the regular expression with a small scanner that:

• treats single and double quotes as grouping characters;
• removes the surrounding quotes;
• supports quotes within a parameter, including -gcflags="all=-N -l";
• adds no dependency.

The table-driven tests cover the reported -tags case, the double-quoted equivalent, attached quotes, and whitespace handling.

Validation:

• go test ./util/sh -run TestSplitParameters -count=1 -v
• go test ./cmd/... ./pkg/... ./util/...
• go vet ./...
• make style
• make unused
• make lint

The full root-package test run also reaches two environment/pre-existing failures: the extldflags integration assertion reproduces on the clean base, and the crossbuild test requires Docker.

Fixes #172

@kakkoyun