Update to goldmark 1.3.3 (#15059) (#15061)

Backport #15059

Signed-off-by: Andrew Thornton <art27@cantab.net>

vendor/github.com/yuin/goldmark/parser/parser.go

@@ -138,6 +138,9 @@ type Context interface {
 	// Get returns a value associated with the given key.
 	Get(ContextKey) interface{}
 
+	// ComputeIfAbsent computes a value if a value associated with the given key is absent and returns the value.
+	ComputeIfAbsent(ContextKey, func() interface{}) interface{}
+
 	// Set sets the given value to the context.
 	Set(ContextKey, interface{})
 
@@ -252,6 +255,15 @@ func (p *parseContext) Get(key ContextKey) interface{} {
 	return p.store[key]
 }
 
+func (p *parseContext) ComputeIfAbsent(key ContextKey, f func() interface{}) interface{} {
+	v := p.store[key]
+	if v == nil {
+		v = f()
+		p.store[key] = v
+	}
+	return v
+}
+
 func (p *parseContext) Set(key ContextKey, value interface{}) {
 	p.store[key] = value
 }