[mv3] Improve management of regex-based rules

- Make place for more dynamic regex-based rules when there is a
  risk session regex-based rules could interfere

- Do not prune `allow` strict-block rules as they do not contribute
  toward the overall regex-based rule count

Possibly related issue:
uBlockOrigin/uBOL-home#556

Author: gorhill

platform/mv3/extension/js/ruleset-manager.js

@@ -168,19 +168,20 @@ async function updateRegexRules(currentRules, addRules, removeRuleIds) {
 
 async function updateDynamicRules() {
     const currentRules = await dnr.getDynamicRules();
-    const addRules = [];
-    const removeRuleIds = [];
 
     // Remove potentially left-over rules from previous version
+    const removeRuleIds = [];
     for ( const rule of currentRules ) {
         if ( rule.id >= SPECIAL_RULES_REALM ) { continue; }
         removeRuleIds.push(rule.id);
         rule.id = 0;
     }
 
+    const addRules = [];
     await updateRegexRules(currentRules, addRules, removeRuleIds);
     if ( addRules.length === 0 && removeRuleIds.length === 0 ) { return; }
 
+    const dynamicRegexCountBefore = dynamicRegexCount;
     dynamicRegexCount = 0;
     let ruleId = 1;
     for ( const rule of addRules ) {
@@ -190,6 +191,11 @@ async function updateDynamicRules() {
     if ( dynamicRegexCount !== 0 ) {
         ubolLog(`Using ${dynamicRegexCount}/${dnr.MAX_NUMBER_OF_REGEX_RULES} dynamic regex-based DNR rules`);
     }
+    // If we increase the number of dynamic regex rules, reset session rules to
+    // reduce risk of hitting maximum regex count
+    if ( dynamicRegexCount > dynamicRegexCountBefore ) {
+        await clearSessionRules();
+    }
 
     const response = {};
 
@@ -339,8 +345,11 @@ async function updateSessionRules() {
     let regexCount = dynamicRegexCount;
     let ruleId = 1;
     for ( const rule of addRulesUnfiltered ) {
-        if ( rule?.condition.regexFilter ) { regexCount += 1; }
-        rule.id = regexCount < maxRegexCount ? ruleId++ : 0;
+        rule.id = ruleId++;
+        if ( Boolean(rule?.condition.regexFilter) === false ) { continue; }
+        regexCount += 1;
+        if ( regexCount < maxRegexCount ) { continue; }
+        rule.id = 0;
     }
     sessionRegexCount = regexCount - dynamicRegexCount;
     const addRules = addRulesUnfiltered.filter(a => a.id !== 0);
@@ -367,6 +376,13 @@ async function updateSessionRules() {
     return response;
 }
 
+async function clearSessionRules() {
+    const currentRules = await dnr.getSessionRules();
+    if ( currentRules.length === 0 ) { return; }
+    const removeRuleIds = currentRules.map(a => a.id);
+    return dnr.updateSessionRules({ removeRuleIds });
+}
+
 /******************************************************************************/
 
 async function getEffectiveSessionRules() {