Labels: add fake versions of SymbolTable apis

So we can use them where necessary for internlabels implementation.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

model/labels/labels.go

@@ -420,11 +420,32 @@ type ScratchBuilder struct {
 	add Labels
 }
 
+// Symbol-table is no-op, just for api parity with dedupelabels.
+type SymbolTable struct{}
+
+func NewSymbolTable() *SymbolTable { return nil }
+
+func (t *SymbolTable) Len() int { return 0 }
+
 // NewScratchBuilder creates a ScratchBuilder initialized for Labels with n entries.
 func NewScratchBuilder(n int) ScratchBuilder {
 	return ScratchBuilder{add: make([]Label, 0, n)}
 }
 
+// NewBuilderWithSymbolTable creates a Builder, for api parity with dedupelabels.
+func NewBuilderWithSymbolTable(_ *SymbolTable) *Builder {
+	return NewBuilder(EmptyLabels())
+}
+
+// NewScratchBuilderWithSymbolTable creates a ScratchBuilder, for api parity with dedupelabels.
+func NewScratchBuilderWithSymbolTable(_ *SymbolTable, n int) ScratchBuilder {
+	return NewScratchBuilder(n)
+}
+
+func (b *ScratchBuilder) SetSymbolTable(_ *SymbolTable) {
+	// no-op
+}
+
 func (b *ScratchBuilder) Reset() {
 	b.add = b.add[:0]
 }

model/labels/labels_stringlabels.go

@@ -681,3 +681,24 @@ func (b *ScratchBuilder) Overwrite(ls *Labels) {
 	marshalLabelsToSizedBuffer(b.add, b.overwriteBuffer)
 	ls.data = yoloString(b.overwriteBuffer)
 }
+
+// Symbol-table is no-op, just for api parity with dedupelabels.
+type SymbolTable struct{}
+
+func NewSymbolTable() *SymbolTable { return nil }
+
+func (t *SymbolTable) Len() int { return 0 }
+
+// NewBuilderWithSymbolTable creates a Builder, for api parity with dedupelabels.
+func NewBuilderWithSymbolTable(_ *SymbolTable) *Builder {
+	return NewBuilder(EmptyLabels())
+}
+
+// NewScratchBuilderWithSymbolTable creates a ScratchBuilder, for api parity with dedupelabels.
+func NewScratchBuilderWithSymbolTable(_ *SymbolTable, n int) ScratchBuilder {
+	return NewScratchBuilder(n)
+}
+
+func (b *ScratchBuilder) SetSymbolTable(_ *SymbolTable) {
+	// no-op
+}