[FIX] runtime: make error recovery more robust

The error recovery process is necessary, but is particularly subtle. An
error may occur basically any time some user code is called, which may
leave the internal owl state in an invalid situation.

In this commit, we try to improve Owl behaviour when a crash occurs in a
onMounted hook. Before this commit, it was possible for other component
mounted hooks to be called even though the component was not mounted, or
for willUnmount hooks to be called even though the component was
mounted, but its onMounted hooks had not been called.

All these situations need to be handled when we catch an error. In this
commit, we try to clean more internal state in the error handling code,
to make Owl more consistent.

tests/components/__snapshots__/error_handling.test.ts.snap

@@ -1191,6 +1191,135 @@ exports[`can catch errors error in mounted on a component with a sibling (proper
 }"
 `;
 
+exports[`can catch errors error in onMounted, graceful recovery 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(null, false, false, false, []);
+  
+  return function template(ctx, node, key = \\"\\") {
+    const Comp1 = ctx['component'];
+    return toggler(Comp1, comp1({}, (Comp1).name + key + \`__1\`, node, this, Comp1));
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery 2`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(\`Child\`, true, false, false, []);
+  const comp2 = app.createComponent(\`Boom\`, true, false, false, []);
+  
+  return function template(ctx, node, key = \\"\\") {
+    const b2 = text(\`parent\`);
+    const b3 = comp1({}, key + \`__1\`, node, this, null);
+    const b4 = comp2({}, key + \`__2\`, node, this, null);
+    return multi([b2, b3, b4]);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery 3`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`abc\`);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery 4`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`boom\`);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery 5`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`def\`);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery, variation 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(null, false, false, false, []);
+  
+  return function template(ctx, node, key = \\"\\") {
+    let b2, b3;
+    b2 = text(\`R\`);
+    if (ctx['state'].gogogo) {
+      const Comp1 = ctx['component'];
+      b3 = toggler(Comp1, comp1({}, (Comp1).name + key + \`__1\`, node, this, Comp1));
+    }
+    return multi([b2, b3]);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery, variation 3`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(\`Child\`, true, false, false, []);
+  const comp2 = app.createComponent(\`Boom\`, true, false, false, []);
+  
+  return function template(ctx, node, key = \\"\\") {
+    const b2 = text(\`parent\`);
+    const b3 = comp1({}, key + \`__1\`, node, this, null);
+    const b4 = comp2({}, key + \`__2\`, node, this, null);
+    return multi([b2, b3, b4]);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery, variation 4`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`abc\`);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery, variation 5`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`boom\`);
+  }
+}"
+`;
+
+exports[`can catch errors error in onMounted, graceful recovery, variation 6`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`def\`);
+  }
+}"
+`;
+
 exports[`can catch errors onError in class inheritance is called if rethrown 1`] = `
 "function anonymous(app, bdom, helpers
 ) {