api/go1.16: add go/build/constraint APIs

These APIs were added in CL 240604 as part of an approved proposal. It
was submitted after the initial api/go1.16.txt creation.

For #41184
For #43407

Change-Id: Ifb54df2b61c554c32bd9d17afbb74f4e42e0b228
Reviewed-on: https://go-review.googlesource.com/c/go/+/287412
Trust: Alexander Rakoczy <[email protected]>
Run-TryBot: Alexander Rakoczy <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: toothrot

api/go1.16.txt

@@ -232,6 +232,35 @@ pkg go/build, type Package struct, TestEmbedPatterns []string
 pkg go/build, type Package struct, TestEmbedPatternPos map[string][]token.Position
 pkg go/build, type Package struct, XTestEmbedPatterns []string
 pkg go/build, type Package struct, XTestEmbedPatternPos map[string][]token.Position
+pkg go/build/constraint, func IsGoBuild(string) bool
+pkg go/build/constraint, func IsPlusBuild(string) bool
+pkg go/build/constraint, func Parse(string) (Expr, error)
+pkg go/build/constraint, func PlusBuildLines(Expr) ([]string, error)
+pkg go/build/constraint, method (*AndExpr) Eval(func(string) bool) bool
+pkg go/build/constraint, method (*AndExpr) String() string
+pkg go/build/constraint, method (*NotExpr) Eval(func(string) bool) bool
+pkg go/build/constraint, method (*NotExpr) String() string
+pkg go/build/constraint, method (*OrExpr) Eval(func(string) bool) bool
+pkg go/build/constraint, method (*OrExpr) String() string
+pkg go/build/constraint, method (*SyntaxError) Error() string
+pkg go/build/constraint, method (*TagExpr) Eval(func(string) bool) bool
+pkg go/build/constraint, method (*TagExpr) String() string
+pkg go/build/constraint, type AndExpr struct
+pkg go/build/constraint, type AndExpr struct, X Expr
+pkg go/build/constraint, type AndExpr struct, Y Expr
+pkg go/build/constraint, type Expr interface, Eval(func(string) bool) bool
+pkg go/build/constraint, type Expr interface, String() string
+pkg go/build/constraint, type Expr interface, unexported methods
+pkg go/build/constraint, type NotExpr struct
+pkg go/build/constraint, type NotExpr struct, X Expr
+pkg go/build/constraint, type OrExpr struct
+pkg go/build/constraint, type OrExpr struct, X Expr
+pkg go/build/constraint, type OrExpr struct, Y Expr
+pkg go/build/constraint, type SyntaxError struct
+pkg go/build/constraint, type SyntaxError struct, Err string
+pkg go/build/constraint, type SyntaxError struct, Offset int
+pkg go/build/constraint, type TagExpr struct
+pkg go/build/constraint, type TagExpr struct, Tag string
 pkg html/template, func ParseFS(fs.FS, ...string) (*Template, error)
 pkg html/template, method (*Template) ParseFS(fs.FS, ...string) (*Template, error)
 pkg io, func NopCloser(Reader) ReadCloser