[FIX] web: display signatures in signature fields

**Before this commit**
Since [1], the signature field only display placeholder
signatures when it has a value.

**Explanation**
The commit [1] removes the props "value" from the standard field props.
The signature field missed an adaptation.

**After this commit**
The issue is fixed and a test has been written.

[1] 688986f888
opw-3335655

closes odoo/odoo#123463

X-original-commit: 4edc5e3326cc92e9adf4f2512af1e85382108bb3
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>
Signed-off-by: Bruno Boi (boi) <boi@odoo.com>

addons/web/static/src/views/fields/signature/signature_field.js

@@ -43,9 +43,9 @@ export class SignatureField extends Component {
     }
 
     get getUrl() {
-        const { name, previewImage, record, value } = this.props;
-        if (this.state.isValid && value) {
-            if (isBinarySize(value)) {
+        const { name, previewImage, record } = this.props;
+        if (this.state.isValid && this.value) {
+            if (isBinarySize(this.value)) {
                 return url("/web/image", {
                     model: record.resModel,
                     id: record.resId,
@@ -63,9 +63,9 @@ export class SignatureField extends Component {
     }
 
     get sizeStyle() {
-        let { width, height, value } = this.props;
+        let { width, height } = this.props;
 
-        if (!value) {
+        if (!this.value) {
             if (width && height) {
                 width = Math.min(width, this.displaySignatureRatio * height);
                 height = width / this.displaySignatureRatio;
@@ -86,6 +86,10 @@ export class SignatureField extends Component {
         return style;
     }
 
+    get value() {
+        return this.props.record.data[this.props.name];
+    }
+
     onClickSignature() {
         if (!this.props.readonly) {
             const nameAndSignatureProps = {

addons/web/static/src/views/fields/signature/signature_field.xml

@@ -2,7 +2,7 @@
 <templates xml:space="preserve">
 
     <t t-name="web.SignatureField" owl="1">
-        <t t-if="props.record.data[props.name]">
+        <t t-if="value">
             <img class="o_signature img img-fluid"
                 alt="Binary file"
                 t-att-src="getUrl"