[FIX] compiler: correctly escape special characters in template literals

Previously, there were a few places where the compiler would create
strings from template content and emit them as template literals, but
didn't properly escape characters or character sequences with special
meanings, in particular: backslashes, backticks, and interpolation
sigils.

This commit fixes this in:
- block creation (interpolation sigils were not escaped)
- text node creation (no escaping was performed)
- comment not creation (no escaping was performed)
- default values for t-esc (no escaping was performed)
- body of a t-set (no escaping was performed)

tests/compiler/__snapshots__/comments.test.ts.snap

@@ -1,5 +1,38 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`comments comment node with backslash at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return comment(\` \\\\\\\\ \`);
+  }
+}"
+`;
+
+exports[`comments comment node with backtick at top-level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return comment(\` \\\\\` \`);
+  }
+}"
+`;
+
+exports[`comments comment node with interpolation sigil at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return comment(\` \\\\\${very cool} \`);
+  }
+}"
+`;
+
 exports[`comments only a comment 1`] = `
 "function anonymous(app, bdom, helpers
 ) {

tests/compiler/__snapshots__/simple_templates.test.ts.snap

@@ -341,6 +341,39 @@ exports[`simple templates, mostly static template with t tag with multiple conte
 }"
 `;
 
+exports[`simple templates, mostly static text node with backslash at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`\\\\\\\\\`);
+  }
+}"
+`;
+
+exports[`simple templates, mostly static text node with backtick at top-level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`\\\\\`\`);
+  }
+}"
+`;
+
+exports[`simple templates, mostly static text node with interpolation sigil at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(\`\\\\\${very cool}\`);
+  }
+}"
+`;
+
 exports[`simple templates, mostly static two t-escs next to each other 1`] = `
 "function anonymous(app, bdom, helpers
 ) {

tests/compiler/__snapshots__/t_esc.test.ts.snap

@@ -1,5 +1,41 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`t-esc default with backslash at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { withDefault } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(withDefault(undefined, \`\\\\\\\\\`));
+  }
+}"
+`;
+
+exports[`t-esc default with backtick at top-level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { withDefault } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(withDefault(undefined, \`\\\\\`\`));
+  }
+}"
+`;
+
+exports[`t-esc default with interpolation sigil at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { withDefault } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(withDefault(undefined, \`\\\\\${very cool}\`));
+  }
+}"
+`;
+
 exports[`t-esc div with falsy values 1`] = `
 "function anonymous(app, bdom, helpers
 ) {

tests/compiler/__snapshots__/t_set.test.ts.snap

@@ -1,5 +1,50 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`t-set body with backslash at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { isBoundary, withDefault, setContextValue } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    ctx = Object.create(ctx);
+    ctx[isBoundary] = 1
+    setContextValue(ctx, \\"value\\", \`\\\\\\\\\`);
+    return text(ctx['value']);
+  }
+}"
+`;
+
+exports[`t-set body with backtick at top-level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { isBoundary, withDefault, setContextValue } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    ctx = Object.create(ctx);
+    ctx[isBoundary] = 1
+    setContextValue(ctx, \\"value\\", \`\\\\\`\`);
+    return text(ctx['value']);
+  }
+}"
+`;
+
+exports[`t-set body with interpolation sigil at top level 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  let { isBoundary, withDefault, setContextValue } = helpers;
+  
+  return function template(ctx, node, key = \\"\\") {
+    ctx = Object.create(ctx);
+    ctx[isBoundary] = 1
+    setContextValue(ctx, \\"value\\", \`\\\\\${very cool}\`);
+    return text(ctx['value']);
+  }
+}"
+`;
+
 exports[`t-set evaluate value expression 1`] = `
 "function anonymous(app, bdom, helpers
 ) {